Green process innovation: Where we are and where we are going

Environmental pollution has worsened in the past few decades, and increasing pressure is being put on firms by different regulatory bodies, customer groups, NGOs and other media outlets to adopt green process innovations (GPcIs), which include clean technologies and end-of-pipe solutions. Although considerable studies have been published on GPcI, the literature is disjointed, and as such, a comprehensive understanding of the issues, challenges and gaps is lacking. A systematic literature review (SLR) involving 80 relevant studies was conducted to extract seven themes: strategic response, organisational learning, institutional pressures, structural issues, outcomes, barriers and methodological choices. The review thus highlights the various gaps in the GPcI literature and illuminates the pathways for future research by proposing a series of potential research questions. This study is of vital importance to business strategy as it provides a comprehensive framework to help firms understand the various contours of GPcI. Likewise, policymakers can use the findings of this study to fill in the loopholes in the existing regulations that firms are exploiting to circumvent taxes and other penalties by locating their operations to emerging economies with less stringent environmental regulations.

In the developed world, firms are supposed to adhere to an emission cap and are penalised with carbon tariffs based on emission leakages. Although the industrialised nations in the first world have taken significant policy steps to fight the emissions generated in the production processes, developing economies have chosen to prioritise their economic goals instead (Masoudi & Zaccour, 2013). This tendency has led to the Pollution Haven Hypothesis (PHH), in which firms exploit these loopholes by shifting their operations to developing countries, thereby avoiding the higher tax rates, stricter audits and punishments that they would face on domestic soil (Eyland & Zaccour, 2014).
Faced with criticism and sanctions, the developing countries have started to catch up with the trend and have begun to announce similar policy measures. One such example is China, which has announced a carbon emissions cap and enacted different tax rates on goods produced for domestic consumption and exports separately (Zhao et al., 2014). Furthermore, a separate department has been created under the Ministry of Ecology and Environment to set emission caps and ensure the proper implementation of these and other related policy decisions, thus reflecting the sensitivity and commitment of the Chinese government towards environmental issues (R. Dai & Zhang, 2017). It, therefore, becomes increasingly difficult for firms to relocate production facilities to pollution safe-havens, forcing them to either adopt green technologies or pay additional fines and penalties. Apart from the regulatory measures, normative pressures also exert a significant impact on firms to adopt green process innovations (GPcIs). As customers are becoming more sensitive to environmental issues, they are demanding an end to polluting technologies while calling for products made using green technologies (Huang et al., 2016). Therefore, firms have to adopt green production technologies and related equipment in their production process to retain their customer base, whose interest in such technologies has been increasing exponentially (R. Dai & Zhang, 2017).
As a sub-dimension of green innovation, GPcI has received significant attention from the researcher community. However, the literature is disjointed, with different terms being used to discuss production-related issues, which include but are not limited to green innovation, GPcI, eco-process innovation, environmental process innovation, clean process innovation and so on. Furthermore, the scope of issues discussed is similarly diffuse as research has been published in heterogeneous journals ranging from policy matters to consumer behaviour. Although one noteworthy bibliometric review has been conducted on green innovation (Karimi Takalo et al., 2021), the selected literature included green product innovation, green managerial innovations and green marketing innovations in addition to GPcI (Abu Seman et al., 2019), making its scope too broad to capture the issues, challenges and gaps specific to the GPcI literature. In comparison, the current study systematically reviews the relevant literature on GPcI published to date to provide a comprehensive picture of the issues and challenges faced by firms in their transition from conventional polluting and inefficient technologies to GPcI. A systematic literature review (SLR) study not only helps in synthesising the literature to broaden our understanding of relevant issues but also helps in developing a comprehensive framework that guides the management and other external stakeholders. In line with these arguments, the present study sets out four research questions (RQs): RQ1. What is the research profile of prior relevant studies published on GPcI? RQ2.
What are the different research themes and focus areas studied in the selected studies? RQ3. What are the various limitations and gaps in the prior literature? RQ4. In what ways can the research and practice in GPcI be taken forward?
To address these RQs, we utilised stringent systematic review criteria set forth by Dhir et al. (2020), Seth et al. (2020), T. M. et al. (2021) and Talwar et al. (2020). RQ1 was addressed by extracting the research profiles of the selected studies after explaining the conceptual boundary, database selected, keywords used and shortlisting criteria. To address RQ2, we organised the studies into seven themes, based on our understanding from the content analysis, composing of strategic response, organisational learning, institutional pressures, structural issues, outcomes, barriers and methodological choices. To answer RQ3, we critically analysed the selected studies and presented theme-based open research gaps as well as the associated potential RQs. Finally, we responded to RQ4 by (a) developing a framework that aims to provide a high-level picture of the different contours of GPcI and (b) discussing the various implications of this study for business strategy and practice.
As GPcI concerns energy consumption and environmental pollution, its adoption is driven by sustainable development goals. Consequently, the research contribution, in terms of academic papers, has remained largely disjointed with varying audiences. Therefore, the outcomes of this SLR would be of interest to different stakeholder groups, ranging from scholars to policymakers and to people holding significant managerial positions with the discretion to alter their firm's course of action. Scholars can further take note of what has been done and what needs to be done regarding research contributions.
The practitioner, meanwhile, can get a holistic understanding of the various issues, challenges and potential benefits of GPcI to make better, more informed decisions. The study is of immense benefit for policymakers, especially in the developing world, as they can utilise the findings to bring course-altering regulations and penalties so that the adoption of GPcI by firms is hastened.
This SLR is organised into seven sections. In this first section, we outlined the introduction; in the second section, the scope and boundary conditions for this study are set. The third section focuses on the methodology used to identify relevant studies, whereas the fourth section discusses the emergent themes in the GPcI literature. In the fifth section, we highlight the gaps in this literature and the potential RQs that future researchers can then address. The sixth section provides the framework of this study, whereas the seventh section concludes our findings with appropriate implications for business strategy and practice.

| SCOPE OF THE REVIEW
GPcI refers to the adoption and implementation of technologies that reduce energy consumption in the production processes (Salvad o et al., 2012). More specifically, GPcI involves making a transition from conventional energy sources to bioenergy so as to reduce the total energy consumption and greenhouse emissions (Kivimaa & Kautto, 2010). The literature on green innovation has divided GPcI into clean technologies and end-of-pipe solutions (Chiou et al., 2011). Clean technologies are designed to efficiently utilise resources and energy while reducing emissions in the production processes, whereas end-of-pipe solutions are tailored to capture and treat emissions and pollution at the end of the production process (Berrone & Gomez-Mejia, 2009). Although end-of-pipe solutions may not be as essential in the overall production process as clean technologies, they significantly reduce emissions and improve the waste management practices of firms and nations, leading to cleaner water bodies and the overall natural environment (Chiou et al., 2011). This study, therefore, focuses on GPcI for two reasons. First, based on our understanding from the green innovation literature, firms consider offering green products easier than switching to GPcI due to the high costs involved and longer pay-back periods (Kassinis & Vafeas, 2006). Therefore, it is crucial to unravel the various factors that can help the practitioner and policymakers take adequate steps to exert pressure on firms to switch to GPcI. Second, although a few noteworthy SLR studies have been conducted on green product innovations (e.g., Dangelico, 2015), to the best of our understanding, no SLR has yet been undertaken on GPcI to date.
To select the relevant studies on GPcI, we followed a two-step procedure. In the first step, we included research articles that used 'green innovation' in the title but measured GPcI in the paper. Second, the literature on GPcI has used different terms for process innovation, including eco-process innovation, eco process innovation, green technology innovation, clean technology innovation, sustainable process innovation and environmental process innovation. We compared the definition and scale items utilised in these studies and, based on our understanding of the results, either included or excluded the articles. Specifically, this SLR includes those studies ( Figure 1) that are congruent with the definition and scale measures of GPcI studies.

| RESEARCH METHOD
The aim of this study was to undertake a comprehensive and critical review of the studies that have been published on GPcI using the SLR methodology. This methodology was chosen due to its interdisciplinary acceptance as the preferred method of reviewing studies, especially across different areas of management research , and its ability to reproduce similar results (Seth et al., 2020). There are different suggestions in the literature about the steps to be followed while conducting the SLR to ensure that future similar studies can replicate or extend it Seth et al., 2020;Talwar et al., 2020;T. M. et al., 2021). The current study is in line with the arguments of these researchers; accordingly, we have utilised a four-step process, which includes: Step I: Planning the review; Step II: Specifying the screening criteria; Step III: Data extraction; and Step IV: Data execution.

| Planning the review
GPcI is a subtopic within the green innovation literature. With the aim to include the maximum number of studies on GPcI, we began by searching two keywords: 'green process innovation' and 'green AND process innovation'. These keywords were initially searched on Google Scholar before the first 100 results were analysed to update our list of keywords. We then searched the leading journals on energy, green innovation and sustainability to assess whether our keywords were exhaustive or not. To ensure a bias-free research profiling of the studies, we assembled a review panel consisting of one professor, one practitioner and two researchers. After consulting this panel, we further added eco-process innovation, eco process innovation, green technology innovation, clean technology innovation, sustainable process innovation and environmental process innovation to the list. Finally, the selected keywords were used to search and retrieve studies from the Scopus and Web of Science (WoS) databases as they include a comprehensive list of reputed journal articles, especially in the field of the social sciences (Mongeon & Paul-Hus, 2016).

| Screening criteria
After the keywords selection, exclusion and inclusion criteria were specified to screen the studies. The inclusion criteria required the studies to be (a) peer-reviewed, (b) published in the English language on or before the 17th of January 2021 and (c) primarily focused on GPcI. The exclusion criteria mandated the removal of studies that were (a) not congruent with GPcI; (b) not directly related with GPcI, for example, green process innovations; (c) appearing twice with matching author, title, volume, issue number and digital object identifier (DOI); and (d) reviews, conceptual papers, thesis papers, editorials and conference proceedings. F I G U R E 1 Scope of this study

| Data extraction
Utilising * and Boolean logic and 'OR' and 'AND' connectors, the keywords were converted into search strings ( Figure 2). A total of 619 articles published in the English language were found, which included 419 articles in Scopus and 200 articles in the WoS database.
After applying the pre-specified inclusion and exclusion criteria, 240 duplicate articles were identified and excluded using Microsoft Excel spreadsheets. The remaining 379 articles were further screened based on the exclusion criteria, and 242 articles were further excluded from the list. At this stage, two authors of this study further synthesised the remaining studies individually using the pre-specified exclusion criteria. They were allowed to share their results once they were done screening the articles so that they could discuss any differences in the shortlisting procedure to arrive at a consensus. After several rounds of discussions, the researchers finally agreed to remove 61 articles, which they found to be inconsistent, from the list. The final list of 76 studies was then examined by one practitioner and a professor having experience in green innovations, who then agreed with the filtered down list. However, while running a backward and forward search of these articles, the authors further extracted four articles that were not identified in our initial search and added them to the list.

| Research profiling
The research has been presented in terms of different statistics related to the year-wise publications on GPcI, publishing journals, the geographic scope of studies, theoretical frameworks used, methods and sample used, respondent profile and the top-cited journals, as these help in better understanding the GPcI literature conducted over the years. The review suggests that increased scholarly attention has been paid to GPcI research over the past 3 years and that the trend is growing (see Figure 3). Most of the studies (see Figure 4) have been published in the Journal of Cleaner Production, Sustainability and Business Strategy and the Environment, highlighting the strategic focus of researchers. However, most of the studies have been conducted in China (see Figure 5), which limits our understanding of the issues and challenges faced by firms in other economies. The selected studies have mostly utilised stakeholder theory, the resource-based view (RBV) and institutional theory to understand the various antecedents, consequences and issues related to GPcI (see Figure 6). Although regression and structural equation modelling techniques (see Figure 7) have mostly been used to analyse the data, most of the results of these analyses are based on primary data (Figure 8), collected mostly from top-level management (see Figure 9), which limits our understanding and the generalisability of the results. Finally, Figure 10 reveals the top-cited journals, highlighting their contribution to green innovation in general and GPcI in particular.

| THEMATIC FOCI
The selected studies (N = 80) of this review were critically analysed with a focus on better understanding the various antecedents, consequences and challenges of GPcI. To synthesise this diverse set of studies, we undertook a thorough review and content analysis of each paper to unravel common themes, in line with the recently published SLR studies Seth et al., 2020;Talwar et al., 2020).
F I G U R E 2 Systematic literature review methodology adopted to select relevant articles. GPcI, green process innovation; WoS, Web of Science Year-wise distribution of the selected studies published on green process innovation F I G U R E 4 Journal-wise distribution of the selected studies published on green process innovation F I G U R E 5 The geographic scope of studies conducted on green process innovation F I G U R E 6 The theoretical framework utilised by the researchers in their studies on green process innovation F I G U R E 7 Graphical representation of the methods used in the selected green process innovation studies We then followed a three-step procedure to minimise the bias associated with the thematic segregation of studies. First, two authors of this study conducted the open coding of the selected studies using the Microsoft Excel 2019 program. In the second step, inductive and deductive reasoning were utilised to conduct axial coding to identify relationships among the open codes. In the third step, we requested a professor and a practitioner with experience in green innovationrelated topics to review the themes identified in the second step. The experts were largely in agreement with the developed themes, which suggests that the researchers had rigorously discussed the open and axial coding-related issues. However, based on the feedback received from the experts, some minor corrections were made, and a total of seven themes were finalised (see Figure 11). The developed themes were strategic response, organisational learning, institutional pressures, barriers, structural issues, outcomes and reflections on the methodological choices adopted by the selected studies of this review.

| Strategic response
In the ever-changing business landscape, firms must employ different strategic responses to survive. Strategic responses refer to the decisions taken by firms to align their operations to the external environment (Johnson et al., 2005). These responses are broadly classified into reactive and proactive responses (Arag on-Correa, 2000). Firms with a reactive response tend merely to comply with compulsory requirements and delay action until the very end of the process (Haque et al., 2016), as the formalisation of environmental objectives has not yet been defined and integrated into the overall business strategy (Perego & Hartmann, 2009). However, firms that follow a more proactive response voluntarily take up environmentally friendly practices and even exceed the minimum regulatory compliances (Torugsa et al., 2013). The prior literature on GPcI has studied five different types of strategic responses, which include environmental orientation, environmental ethics, technological implementation, environmental corporate social responsibility (ECSR) and political connections, as discussed below.

| Environmental orientation
Environmental orientation refers to the managerial recognition of the environmental problems surrounding the firm (Banerjee, 2002).
Embodied in the mission statement of the firm, environmental orientation is often segregated into internal and external orientations.
Internal orientation concerns the values and norms of the firm, which researchers deem to be a kind of pro-environmental culture that shapes the strategic vision of the firm and motivates the employees to think in more environmentally friendly ways (Gabler et al., 2015).
External orientation, meanwhile, refers to the attitude of the firm towards environmental conservation (Banerjee, 2002). Such an orientation is shaped by the pressures from various stakeholders by way of regulations and other norms, which force the firm to switch to GPcI (Chan, 2010). Together, internal and external orientations influence the relationship of the firm with its various stakeholders and, as such, play a crucial part in pushing the firm to adopt GPcI (L.

| Environmental ethics
Environmental ethics refer to the integration and formalisation of environmental beliefs into decision-making (Guo et al., 2020). Firms with high environmental ethics are concerned about the degradation of the environment, which prompts them to place greater emphasis on the greening of their production processes (Chang, 2011). Environmental ethics influence the innovation of environmentally friendly technology and operations, which, in turn, results in a competitive advantage for the firm (Schlegelmilch et al., 1996). Therefore, if firms want to enhance their competitive advantage through the development of GPcI, they should invest heavily in raising their environmental ethics (Chang, 2011).

| Technological implementation
Firms are implementing advanced manufacturing technologies (AMTs), which mostly comprise factory automation technologies (Swink & Nair, 2007), to enhance their information sharing and processing capabilities, which, subsequently, has a positive impact on GPcI. AMTs allow the employees to interact more efficiently while facilitating real-time information sharing within the firm (Zairi, 1992).

This swift communication and information flow results in improved
coordination across departments, thereby enhancing the GPcI capabilities of the firm, especially during the initial phases of development (Turkulainen & Ketokivi, 2012). Similarly, AMTs bring automation and computational capabilities together. This synergetic effect then helps in the optimisation of resource utilisation, which, in turn, helps the firm meet environmental regulations (Kong et al., 2016).

| Environmental corporate social responsibility
ECSR refers to the responsibility of the firm for its impact on society (European Commission, 2011). ECSR helps generate slack resources in addition to the resources possessed by the firm. Slack resources reduce the risks and uncertainties inherent in the implementation of GPcI projects (Teece et al., 2016) and, therefore, have become more or less necessary to derive benefits from such innovations (Chiu et al., 2008). Firms that are non-innovative due to financial constraints may be aided through ECSR activities as slack resources can be invested in R&D activities that can then help produce GPcI (Zúñiga-Vicente et al., 2014). The relevant literature on GPcI has identified four main sources of financial slack, including, first, cost savings on the part of fewer material inputs (Arag on-Correa, 1998); second, higher profits due to deductions in taxation and other related subsidies (Forcadell et al., 2021); third, attracting new customers (Choi & La, 2013); and, finally, access to additional funding from investors (Harjoto & Jo, 2015). Therefore, ECSR not only generates a cost advantage and tax rebates for the firm but also attracts additional investments as the overall profitability increases due to the inclusion of new green customers in its total portfolio (Forcadell et al., 2021).

| Corporate political connections
Corporate political connections refer to close relationships with politicians and government officials (Nee & Opper, 2010). Political capital is beneficial for the firms as it extends preferential treatment, taxation benefits and lower regulatory pressures and other beneficial resources (Faccio, 2010). As firms are compelled to adhere to certain regulations, they tend to use their political connections to seek government protection and access to resources that can help the firm sustain its competitive edge over rivals (H. Wang & Qian, 2011). Political capital also has a positive impact on the R&D activities of the firm (Khwaja & Mian, 2005). Furthermore, firms that are politically well connected have better GPcI than non-connected firms, which may be explained by the mitigation of risks due to political capital (Nanda & Rhodes-Kropf, 2013).

| Organisational learning
Firms are increasingly looking at new knowledge sources while refining their existing knowledge to compete with their rivals and comply with the regulations set forth by different governmental and nongovernmental agencies. Firms these days acquire new knowledge by entering into strategic partnerships with alliance partners and suppliers (Manuj et al., 2014). Moreover, the use of Big Data techniques is becoming increasingly popular among firms as it offers rich insights into data (Tien, 2013). The extant literature on GPcI has broadly focused on four issues related to organisations learning. These include absorptive capacity, Big Data, search breadth and depth, and green supplier learning (GSL), which we discuss below.

| Absorptive capacity
A firm's absorptive capacity is its ability to value and assimilate new information and exploit it for commercial ends (Cohen & Levinthal, 1990). Green absorptive capacity plays a crucial role in recognising the external pressures and understanding the mechanisms that can help overcome organisational inertia (Pacheco et al., 2018).
Likewise, absorptive capacity helps in the inter-functional coordination required to assimilate and apply knowledge (Najafi-Tavani et al., 2016). Under high environmental pressures, firms tend to focus on developing intrinsic capabilities so that they can succeed with their GPcI efforts (Lin et al., 2016). As one of the crucial firm-specific capabilities, absorptive capacity instigates the realisation of interorganisational learning. However, the firms' response by way of GPcI relies heavily on their assimilation of supply-side technological and demand-side customer preferences (Brix, 2019). Firms that do not possess the right mix of absorptive capacity are more likely to resist institutional pressures, whereas those that possess higher absorptive capacity are more likely to see the environmental pressures as opportunities and turn them into a competitive advantage (Delmas et al., 2011). Absorptive capacity helps the firm to integrate such pressures into green innovation practices and, therefore, positively influences the development of GPcI (Ben Arfi et al., 2018).

| Big Data
Big Data refers to large volumes of datasets (Hampton et al., 2013) that require special acquisition and application skills to extract meaningful information from them (Tien, 2013). Over the years, data collection and storage capacities, along with the available volumes of data, have increased exponentially, and, as such, traditional methods of drawing meaningful analysis from data have become redundant (Li et al., 2016). Big Data offers access to new information, which can help in decision-making processes (Tien, 2013), but it also requires a significant change in the existing organisational capabilities to utilise it (Braganza et al., 2017).

| Search breadth and depth
The manner in which firms search for external knowledge has been broadly segregated into search breadth and search depth. Search breadth refers to the number of sources that a firm uses in its innovation process (Laursen & Salter, 2006). Firms tend to have a trial-anderror period in which they decide on the number of external partners and channels necessary for improving their innovation capacity. Such diversification helps the firm hedge against the various risks associated with the innovation search (Leiponen & Helfat, 2010) and helps them find a viable combination. Horbach et al. (2013) argued that firms' pursuits of GPcI require more external knowledge sources than other innovations, as the knowledge is heterogeneous and dispersed among various partners. Therefore, the higher the number of external sources is, the better the chances of finding and developing GPcI will be. Search depth, on the other hand, refers to the extent to which firms extract knowledge from different search channels and sources (Laursen & Salter, 2006). As the firm finds a suitable external source or channel, it tends to benefit from it due to the lower transaction costs associated with the deep assimilation of knowledge (Greco et al., 2016). Search depth has a positive impact on the GPcI effort of firms because it facilitates a greater resource and knowledge flow to take place. Increasing the magnitude and frequency of interactive learning helps the firm reap advanced knowledge; therefore, the possibility of switching to GPcI increases significantly (Gonz alez-Moreno et al., 2019).

| Green supplier learning
Learning from green suppliers includes acquiring information pertaining to environmental protection and developing the skills and capabilities required to tackle environmental issues (Fang & Zou, 2010). GSL pushes the firm to align its manufacturing technology to suit the advanced materials, components and services provided by suppliers (Fang & Zou, 2010). Furthermore, GSL helps in developing shared norms and goals for both the manufacturing firm and the supplier, which, in turn, strengthens both parties' green project implementations. GSL allows the manufacturing firm to focus on GPcI, such as by installing green equipment and pollution control systems to demonstrate its commitment to shared environmental goals (T. Feng et al., 2016). However, the impact of GSL on GPcI adoption is conditional to the level of technological turbulence surrounding the firm. Firms operating in highly turbulent environments and constrained by slack resources are likely to focus on external technological demands (M. Song et al., 2005).

| Institutional pressures
The institutional theory posits that firms operate under different regulatory norms and governing bodies (e.g., governmental agencies, nongovernmental organisations, media and other rights groups; Bansal & Clelland, 2004;Campbell, 2007) that collectively govern their actions.
The relevant GPcI literature has studied and discussed three institutional pressures, which include regulatory, normative and imitative pressures.

| Regulatory pressure
Regulatory pressures, also referred to as command and control regulations, are rules that govern the behaviour of firms in an economy (Prajogo et al., 2012). Command and control regulations mandate that all firms adhere to environmental responsibilities while disregarding the cost differentials that exist between them. Such regulations affect market access, product and emissions standards and other production technologies, to name a few. Any disregard for these regulations may expose the firm to administrative punishments and a more stringent inspection procedure (Shen et al., 2020). In the absence of environmental regulations, manufacturing firms tend to avoid GPcI efforts.

| Normative pressure
Pressures from customers and non-governmental agencies, termed normative pressures, prescribe appropriate environmental behaviours for the firm based on societal norms and values (Berrone et al., 2013).
As such, firms are increasingly taking up GPcI in an effort to cater to the environmental-centred demands of the customers (Huang et al., 2016). Likewise, the local community and investors also assess the environmental legitimacy of firms (Bansal & Clelland, 2004), with the media also playing a greater role in this awareness (X. Chen et al., 2018). As firms acquire and/or develop GPcI, they signal to the customers their willingness and commitment to environmental conservation (Wittstruck & Teuteberg, 2012). The subsequent adaptation of manufacturing processes helps minimise the long-term detrimental effects on the environment due to the firms' production process and, in turn, fosters increased cooperation and support from customers (Chiou et al., 2011).

| Imitative pressure
Imitative pressures originate from the firm's peers and influence the firm's GPcI strategies. As firms increasingly seek to adopt GPcI, they compel other firms operating in similar industries to adopt the same kinds of measures (Carter & Rogers, 2008). When firms lack strategic direction, they tend to imitate the strategic behaviour of their peers (DiMaggio & Powell, 1983), which eventually helps them reduce the risks associated with their decisions. In fact, the most common reason advanced by researchers for the non-adoption of GPcI is the uncertainty associated with such endeavours (Rennings & Rammer, 2011). As the number of firms adopting GPcI increases, this uncertainty decreases as a result, and a network of green firms emerges, which further creates barriers for the non-green firms and affects their competitiveness (Qi et al., 2021).

| Structural issues
Structural issues pertain to the overall hierarchical structure, leadership, culture, roles and skills of employees in a firm (Vial, 2019). Firms usually make changes to their structures to shape or support their strategies (Matt et al., 2015). The relevant literature on GPcI has revealed two major structural issues that warrant the attention of firms, namely, top managerial commitment and awareness and board gender diversity, which are discussed below.

| Top managerial commitment and awareness
The awareness and commitment of top management towards environmental issues is a crucial factor in deciding the strategic path that firms will choose while doing business. The GPcI literature broadly categorises managers' environmental awareness into environmental risk awareness and environmental cost-benefit awareness (Gadenne et al., 2009). Environmental risk awareness refers to the firm's cognisance of its negative impacts on the environment, whereas environmental cost-benefit awareness is the cost advantage that the firm can achieve as a result of eco-friendly innovations (Peng & Liu, 2016).
Both managerial risk awareness and cost-benefit awareness play a positive role in the GPcI process as they allow the managers to focus on environmental issues and create business opportunities while addressing such concerns. Moreover, managers with higher environmental risk awareness tend to choose GPcI, which has the potential to exceed emission targets well-above the thresholds set by regulatory bodies (Liu et al., 2015).
Commitment, on the other hand, signifies the firm's dedication to upholding a relationship and enables the achievement of mutual goals.
The commitment towards green innovations can not only strengthen ecological performance but also enhance cooperation from customers, thereby resulting in higher firm performance (Burki et al., 2018). Top managerial backing is essential for successful environmental management as it plays a crucial role in the adoption and implementation of GPcI (Kearns & Sabherwal, 2006). Furthermore, environmental commitment helps in the refinement of operational and managerial performance, which then translates into a competitive advantage for the firm (Lee, 2009).

| Board gender diversity
Women tend to have stronger environmental preferences than men, which makes their presence on management boards a significant predictor of a firm's environmental actions (He & Jiang, 2019). This generally heightened environmental sensitivity often leads women to comply properly with all ethical codes of conduct (Ibrahim et al., 2009) and stimulate environmentally healthy strategies in the firm (Nadeem et al., 2017). Moreover, women's participation in boards tends to stimulate dialogue and discussions centred around stakeholders' needs via the more participative and democratic leadership style that they tend to cultivate. Therefore, the presence and participation of women in boards enrich the diversity of opinions therein and, as such, help the firm make strategic changes in its operations to suit the environmental needs (Adams & Ferreira, 2009

| Outcomes
Firms adopt GPcI either voluntarily or due to different institutional pressures. Once adopted, however, GPcI generates different performance implications. While synthesising the relevant literature on GPcI, we came across eight different performance outcomes, which include financial performance, brand equity, job satisfaction, competitive advantage, green product success, firm value, energy intensity and emission reduction.

| Financial performance
The adoption of any new technology has performance implications for the firm, and GPcI is no exception. The extant literature has categorised GPcI as consisting of either clean technology or end-of-pipe technologies, both of which have different implications for the firm (Xie et al., 2016). Clean technologies help in the minimisation and elimination of wastage and other pollutions in the production process.
Although investing in clean technologies requires heavy funding, it does reduce the costs of environmental compliance and improve the long-run performance of the firm (Chien & Peng, 2012). Furthermore, clean technology adoption not only reduces harmful environmental impacts but also enhances the performance of the firm by way of cost, speed and flexibility of operations (Klassen & Whybark, 1999).
End-of-pipe technologies, on the other hand, are process technologies that treat pollution at the end of the production process and turn the emissions into manageable substances (del Río Gonz alez, 2005). End-of-pipe technologies have the potential to address regulatory concerns and mitigate the negative effects of production processes on the environment (Frondel et al., 2007). Adopting such technologies has fewer barriers as they usually require fewer adjustments in the existing production processes and technologies possessed by the firm (del Río Gonz alez, 2005). Moreover, end-ofpipe technologies can prove beneficial for the firm in terms of the resource rarity that such technologies offer, as these can add value by way of economic rent to the firm (Hart, 1995). Thus, the adoption of both clean technologies and end-of-process technologies are beneficial not only to the environment but also to the firm as they help in the generation of higher profits and slack resources.

| Firm value
Firm value refers to the net present value of the future cash flows that a firm may generate (Rao et al., 2004). In emerging economies, customers often do not appreciate the firms' green efforts and are less willing to prefer products made through GPcI. The reason for such a tendency is partly explained by the lack of proper awareness among customers about environmental issues as well as by their inability to pay higher prices for products made through such processes (Zhu & Sarkis, 2016). However, firms are also responsible for this to some extent if they are unwilling to commit huge funds to GPcI, which overburdens their balance sheets and reduces their profit margins (Rennings & Rammer, 2011

| Competitive advantage
Adopting GPcI also improves a firm's competitive edge against its rivals (Chang, 2011). Firms investing in clean and end-of-pipe technologies minimise the wastage of resources and improve their productivity, which, in turn, enhances their image in the market (Berry & Rondinelli, 1998). As firms successfully improve their image, they not only strengthen the customer adoption of products and services but also extend the first-mover advantage to themselves, thereby giving them an edge over rival firms (Chang, 2011;Y. S. Chen et al., 2006).

| Brand equity
Brand equity refers to the additional value that a firm extracts from its products due to its brand name, which results in part from customers' awareness about the brand, its strength and uniqueness, as well as its likeability and the customers' experiences with it (Keller, 1993). As firms adopt green innovation strategies, they send a positive signal to customers that allows them to charge higher prices or gain an earlymover advantage in new market segments. These strategies further enable the firm to create strong brand associations and a loyal customer base (Porter & van der Linde, 2017). Accordingly, firms should focus on highlighting the environmental and economic benefits of GPcI in their communications to reap the optimum benefits of brand equity (Amores-Salvad o et al., 2014). However, GPcI is less visible to customers than green product innovations, which is why customers do not always appreciate the firms' efforts to reduce pollution in their production processes. Empirical studies have found that customers are unwilling to bear the extra green energy costs because such measures are a part of the production (Kammerer, 2009). Therefore, such efforts are less likely to create brand equity for the firm (Hillman & Keim, 2001).

| Green product success
Firms are increasingly turning to GPcI partly because of increasing customer awareness about environmental issues (Banerjee et al., 2003). However, addressing such concerns effectively and succeeding at the same time is a daunting task that requires a thorough understanding of both customer and regulatory requirements and environmental ethics (V. Wong et al., 1996). The reduction of resource wastage, cutting down of emissions, reuse of materials and components, and efficient use of energy in the production processes lead to the production of green products, which customers are increasingly demanding (S. K. S. Wong, 2012).

| Job satisfaction
Job satisfaction refers to the employees' evaluation of the conditions present in the job or the benefits that they may obtain from it. Employee satisfaction is essential for the firm as low satisfaction can create a spike in the turnover level, which translates into poor business performance (Iranmanesh et al., 2017). As GPcI warrants the minimisation of pollution, recycling of waste and reuse of materials and components, it requires a unique skill set to achieve this properly (Santamaría et al., 2012). Firms lacking such skilled employees may become burdened with schedules and tasks, which put pressure on their existing workforce and, in turn, create job dissatisfaction (Bohle et al., 2011). Furthermore, as different training programmes are frequently scheduled to enhance the skills required for GPcI, the resultant increase in job intensity drives a higher turnover rate (Loch, 1998).

| Energy intensity
Energy intensity may be defined as the inefficient use of energy in an economy. Major emerging economies like China have struggled to reduce energy intensity over the past few decades. Energy intensity not only puts higher pressures on economic resources but also traps the country in environmental pollution (Fan et al., 2007). As GPcI consumes less energy, it translates into fewer energy costs and higher profits for the firm (Yan et al., 2021). The use of GPcI thus has the potential to increase energy efficiency in an economy while reducing the total energy requirements, thereby leading to increased savings (Y. Chen et al., 2016).

| Emission reduction
Given that the burning of coal and oil and environmental pollution have worsened, and emission levels have reached an all-time high, there are increasing calls worldwide for firms to switch to GPcI so that the environment can be protected from disasters (Du et al., 2019).
Green technologies can effectively cut down emission levels, reduce pollution and improve our ecology (Y. J. Zhang, Peng, et al., 2017).
However, the adoption of such technologies is a daunting task for any economy. In addition, it requires serious policy-making and regulatory efforts by the governments both within and across borders.

| Barriers
GPcI barriers may be defined as the absence of factors required for innovation. The relevant literature has revealed various internal and external factors that act as barriers in the firm's transition to GPcI.
As GPcI requires firms to be innovative, a lack of proper communication mechanisms, poor normative practices, inappropriate human resource practices and lack of commitment from top executives drive employee resistance to such innovations (Zwick, 2002). Therefore, the firms' decision-making bodies are required to make significant changes in their operations, be open to new ideas and allow their employees to try new creative ideas (Williander, 2006). Likewise, a lack of information about market and technological trends also constrains the firms' GPcI adoption. While combating environmental pollution through the reduction in greenhouse gas emissions has become necessary, finding the right technologies that address these changing environmental regulations is challenging for the average firm (Woolman & Veshagh, 2006). Similarly, the lack of adequate customer demand also acts as a barrier to the adoption of GPcI. Firms indulging in green innovations witness low levels of customer demand due to the higher cost of their product offerings. This tendency keeps the firms away from adopting GPcI as such projects require huge capital investments, and profitable returns from such projects take years (Abdullah et al., 2016).

| Methodological choices
The major focus of the selected studies was to examine the impact of different factors on the adoption of GPcI in firms and the consequences of such adoption. Towards this end, the studies have utilised different methods and techniques and engaged various stakeholders.
The discussion, therefore, in this theme will centre around the methods used, the respondents' profile, the sample size, the geographical scope and the theoretical underpinnings.

Methods used
The majority of the studies in this review have tested their hypothesis using primary data, including e-mail surveys (Albort-Morant et al., 2018), face-to-face interviews (F. Zhang & Zhu, 2019), telephone interviews (Kong et al., 2020) and offline surveys (e.g., Cai et al., 2020). Although primary data collection methods help to validate theories, such methods often suffer from social desirability bias and, as such, cast doubt on the generalisability of such findings.
Although a sizeable number of studies also utilised secondary databases, the scope of these is primarily restricted to Chinese samples, thereby necessitating a revalidation in other contexts.

Respondent profile
Most of the studies have collected data from top-level executives, which include CEO/directors (e.g., Burki & Dahlstrom, 2017), senior executives (e.g., Afshar Jahanshahi et al., 2020) and other managers (e.g., Y. S. Chen et al., 2006). Although these respondent groups are well versed with the firm-level issues pertaining to GPcI, the insights and concerns of the lower level managers and other support cannot be neglected.

Sample size
The studies on GPcI have mostly extracted their results on samples below 250 respondents, making it problematic to generalise their results.

Geographic scope
The studies included in this review have mostly focused on China, which highlights the need for similar studies in other contexts and geographies.

Theoretical underpinnings
As evidenced in Figure 6, the selected studies on GPcI have used stakeholder theory, the RBV and institutional theory to understand the various issues and challenges of GPcI. Although these studies offer unique insights into GPcI-related issues, there is a need to utilise other theoretical lenses like organisational learning theories, ambidexterity theory, dynamic capabilities theory, networking and other emerging theories to unveil the challenges and driving factors of GPcI.

| RESEARCH GAPS AND POTENTIAL RQs
Our critical analysis of the extracted themes as well as the research profile of the studies led us to highlight the different gaps in the GPcI literature, which are provided against the various subthemes of this review. These gaps, provided in Table 1, can provide a pathway for future researchers to undertake further research on GPcI, which, in turn, can broaden our understanding of the topic while aid managerial decision-making.

| FRAMEWORK DEVELOPMENT
The content analysis of the studies included in this SLR helped us identify the common strands in the GPcI literature and the various gaps warranting further research investigations. This deep understanding of the GPcI research has allowed us to use inductive logic to form a systems framework for our study (see Figure 12). Proposed by Katz and Kahn (1966), the systems framework includes an inputprocess-output-feedback cycle and the influence of external pressures. According to this theory, the firm processes the inputs into an output and regularly checks if the output is as planned before making any changes to the inputs accordingly. The whole exercise of converting inputs into outputs is largely influenced by external environmental changes. In this study, we utilise the systems theory to build our framework, which we call the 'green process innovation model', which includes (a) institutional pressures, (b) inputs, (c) strategic responses, (d) organisational learning, (e) transformative processes and (f) outcomes.
We first conceptualise GPcI adoption as triggered or influenced by outside institutional pressures, which include regulatory forces, normative pressures and imitative pressures. Regulatory pressures are considered coercive measures because they push the firms to adopt regulations or face monetary and non-monetary punishments. Similarly, customers, media and other NGOs also pressure firms to adopt certain environmental norms, while the firm may voluntarily adopt certain practices under imitative pressures. Collectively, all of these different institutional forces are effective in triggering changes in the behaviours and routines of the firm.
Inputs consist of transformational leadership, organisational culture, green human resource management, managerial awareness and board gender diversity, which represent the various decisions of the firm that have a bearing on the overall production choices, learning programmes, ethical practices and environmental responsiveness. The decisions taken at this stage highlight the overall focus of the firm and, as such, have a significant impact on its strategic responses and organisational learning, which, in turn, influence the transformative processes. For instance, the inclusion of men and women with diverse backgrounds and experiences will reinforce a wide range of acceptable behaviours at the top management team level. A more diverse board will also discuss and take forward different proenvironmental ideas and also reshape the ways that the firm does business. The output of transformative processes includes firm performance, firm value, competitive edge, brand equity, green product success, job satisfaction, energy intensity and emission reduction. The successful implementation of the firm's learning programmes and its pro-environmental strategic responses will have a positive impact on the adoption of GPcI and, in turn, will result in a positive influence on the performance implications of such decisions.
The output, in terms of various performance targets, acts as feedback to the management, who then compares such outputs to their targeted performance. This feedback then helps them in revising their learning programmes and other strategic decisions.
T A B L E 1 Theme-based research gaps and potential research questions

| Theoretical implications
The results of this SLR have important implications for theory. First, as there is a burgeoning number of studies on GPcI, particularly from within the last 5 years, the literature has become disjointed due to the different terms used for GPcI and the heterogeneity in the journals in which such studies have been published. Therefore, this study overcomes these issues and provides a holistic picture of the GPcI literature, which can prove helpful to researchers focusing on GPcI to widen the scope of their investigations.
Second, this SLR has segregated the GPcI literature into several themes, making it easier to visualise the various aspects of GPcI, which can further be used by scholars from different streams of management research to address the different challenges faced by firms, ranging from GPcI adoption to marketing and other related issues.
Third, this study unravels the various theme-based gaps in the GPcI literature and puts forth different RQs that can mitigate them.
Furthermore, this study revealed that GPcI consists of clean technologies and end-of-pipe solutions; however, the broader literature has not discussed the two separately, which limits our understanding of the intricacies of GPcI. Future researchers should take note of this and make efforts to examine both technologies in detail.
Lastly, this study utilised the input-process-output model to present a systems view on GPcI. The model highlights the various input decisions required, the transformative processes involved and the resulting output in terms of the performance implications of GPcI.
Researchers can use this model to empirically verify the impact of different antecedents and moderators in the GPcI process and the impact of such factors on the firm.

| Implications for business strategy and practice
The study has five key implications for managers and practitioners, which are summarised below.
First, the disentanglement of the GPcI literature into different themes provides a comprehensive overview of the topic, which is of F I G U R E 1 2 Green process innovation model. ECSR, environmental corporate social responsibility; HRM, human resource management immense help to firms and practitioners. For instance, the review revealed that while firms are increasingly using Big Data to aid in their decision-making process, it requires making significant structural changes to amplify existing capabilities (Braganza et al., 2017).
Accordingly, the management can reassess their strategies to adapt to such requirements.
Second, the management needs to respond to the changing demands of stakeholders and come up with a better strategic response, which includes changing their orientation from a businesscentric approach to a more environmental-centric approach in addition to clean technological adoption. Likewise, management should focus on ingraining green ethics and ECSR into their organisational culture by explicitly setting policies and accepted behavioural norms at the workplace. Furthermore, the management should focus on developing political connections to lobby for stricter pollution regulations besides green taxes and subsidies. Doing so would further discourage the adoption and usage of non-green production technologies and thus grant the first-mover advantage to green firms.
Third, the managers must understand the value of organisational learning activities in their pursuit of GPcI. Furthermore, they must work on enhancing the external knowledge search and absorptive capacity of their firms, improving their Big Data exploitation techniques and entering into different strategic alliances and partnerships to learn new ways of doing things.
Fourth, although most of the studies included in this review were conducted in China, they still contribute to our understanding of the various dimensions involved in GPcI. However, managerial validation is still needed to unravel the limitations of these research efforts.
Lastly, the review revealed that regulatory, normative and imitative pressures significantly influence firms to adopt GPcI, thereby providing a basis for policymakers to introduce and strengthen such policies. Moreover, governments and other non-governmental agencies across the globe should unite to introduce national and crossnational environmental policies so that the existing loopholes in the system can be closed, and firms not adhering to these policies and adopting GPcI can be penalised through higher taxes, tariffs and sanctions.

| Limitations and future work
This SLR study has provided a comprehensive view of the state of the for GPcI. Although we used a robust set of keywords to maximise the chances of extracting relevant studies, some studies may still have been missed in this process. Likewise, the manual screening and filtering of studies may have been subject to human error. Although we did engage two researchers to do this part separately to minimise any errors and bias involved with such activity, future researchers should devise more robust techniques to tackle these issues.