Short CommunicationProof of concept of the SCR of NOx in a real diesel engine exhaust using commercial diesel fuel and a full size Pt/beta zeolite/honeycomb monolith
Graphical abstract
Introduction
The main drawback of NOx removal on Diesel vehicles is the oxygen excess in the exhaust, and a reducing agent must be fed into the exhaust stream which must react with NOx in the presence of excess O2. Different reducing agents have been studied, most of them at laboratory scale, including H2, CO, different hydrocarbons, ammonia, urea, etc. [1], [2], [3], [4], [5], [6].
In the SCR (Selective Catalytic Reduction) technology [2], [3], the reducing agent is continuously fed into the gas stream and a selective catalyst is used to promote the reaction of the reducing gas with NOx with respect to the unproductive direct O2 combustion.
In the NSRC (NOx Storage and Reduction Catalyst) process [1], [2], [3], the NOx removal process is carried out in cycles of storage and reduction steps. During the storage steps, which occur in normal driving conditions, NOx is chemisorbed on a basic oxide present on the catalyst. During the reduction steps, the reducing gas is fed and reacts with the nitrogen compounds previously stored (and also with O2).
The SCR technology with urea or ammonia is commercially available for heavy-duty vehicles [6], and the NOx removal technologies suitable for cars are now in a step of optimization and improvement [7]. Some previous articles reported NOx removal studies in real diesel exhausts [2], [8], [9], [10], [11], [12], [13]. Copper and platinum titania based monolithic catalysts were tested for the reduction of NOx with hydrocarbons in real diesel conditions [10], [11], Ag/Al2O3 catalysts were tested for NOx reduction with ethanol in a real diesel exhaust [12] and Cu/titanium silicalite (TS-1) zeolite/cordierite honeycomb catalysts were studied for the simultaneous removal of the NOx, hydrocarbons and CO emitted by a stationary diesel engine [13].
From a practical point of view the most convenient reducing agent would be diesel fuel, because it is already on board on the vehicle and additional tanks and filling facilities would not be required.
In one of our previous studies, the SCR of NOx was successfully performed with propene in a real diesel gas stream (in a power bench) by using a Pt/Al2O3 catalyst [9]. Also, it has been demonstrated in laboratory experiments that Pt/zeolite catalysts outperform the behavior of Pt/Al2O3 due to the zeolites' ability of maintaining a high concentration of hydrocarbon in the catalyst [14]. In previous studies, Pt/beta zeolite/honeycomb monolith catalysts, with 1 cm diameter substrates, were prepared and tested in our laboratory for SCR of NOx with propene [15], [16].
The goal of the current study is to demonstrate that the SCR of NOx can be performed in a real diesel exhaust stream by commercial diesel fuel and using a full size Pt/beta zeolite/honeycomb monolith catalyst.
Section snippets
Catalyst preparation
A cordierite honeycomb monolith supplied by Corning was used as catalyst supports (14.4 cm diameter; 14 cm length; 400 cpsi).
Beta zeolite was loaded into the honeycomb monolith by dip-coating [17], [18], [19] with a water suspension of 9 wt.% commercial powder ammonia beta zeolite (Zeolyst International), 0.4 wt.% surfactant (Teepol) and 0.2 wt.% binder (a 40 wt.% suspension of colloidal silica in water; Ludox AS-40).
To obtain a homogeneously dispersed mixture, the slurry was stirred with a
Results and discussion
Fig. 2 compiles the catalytic test results obtained in SCR experiments. THC and CO removal increased with temperature (Fig. 2a and b, respectively) and NOx removal (Fig. 2c) followed a typical volcano-shape profile, with maxima at 250 °C for all THC inlet concentrations studied. The production of NO2 (data not shown for the sake of brevity) by catalytic oxidation of NO is low in all experiments, that is, the NO2 percentage with regard to total NOx is always lower than 10%. This behavior is
Conclusions
The results of this study demonstrated that the SCR of NOx can be performed in a real diesel exhaust stream with commercial diesel fuel by using a full size Pt/beta zeolite/honeycomb monolith catalyst.
The SCR behavior observed in the real exhaust with commercial diesel fuel was similar to that typically reported in laboratory experiments performed with model hydrocarbons. Typical NOx removal volcano-shape profiles, with maxima at 250 °C, were obtained, with an optimum THC concentration of 3000
Acknowledgments
The authors thank the financial support of Generalitat Valenciana (Project Prometeo 2009/047), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and the Spanish Ministry of Science and Innovation (Project CIT-420000-2009-48), and EU for the FEDER resources.
References (22)
- et al.
Appl. Catal. B Environ.
(1997) - et al.
Microporous Mesoporous Mater.
(1999) - et al.
Catal. Today
(2012) - et al.
Catal. Today
(2002) - et al.
Appl. Catal. A Gen.
(2009) - et al.
Catal. Today
(1998) - et al.
Environ. Pollut.
(2007) - et al.
Catal. Today
(2004) Appl. Catal. B Environ.
(2007)- et al.
Appl. Catal. B Environ.
(2005)
Appl. Catal. A Gen.
Cited by (15)
Technological Applications of Honeycomb Monoliths in Environmental Processes: A review
2020, Process Safety and Environmental ProtectionEffects of Cu loading and zeolite topology on the selective catalytic reduction with C<inf>3</inf>H<inf>6</inf> over Cu/zeolite catalysts
2019, Journal of Industrial and Engineering ChemistryCitation Excerpt :Among the various exhaust gases emitted from vehicles, nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbons (HCs), and particulate matter (PM) are controlled by strict emissions regulations. The representative techniques for NOx abatement are NOx storage-reduction (NSR) [1–3] and selective catalytic reduction using ammonia (NH3-SCR) [4–6] or hydrocarbon (HC-SCR) [7–13] as a reducing agent. Taking the cost and on-board catalytic configuration into account, the HC-SCR technique has been considered to be the most promising candidate for NOx reduction.
Evaluation of the real-time de-NO<inf>x</inf> performance characteristics of a LNT-equipped Euro-6 diesel passenger car with various vehicle emissions certification cycles
2017, EnergyCitation Excerpt :To meet the specified NOx emissions regulations in laboratory and RDE operating conditions, the NOx storage capacity and regeneration frequency models in the LNT system should be matched. In general, LNT systems have a limited NOx reduction efficiency compared to SCR catalysts because LNT devices require rich air-to-fuel operation (λ < 1) during the de-NOx process using injection timing retardation in diesel engines, which causes unstable engine operation and increasing fuel penalties [5,22,25,28,41–49]. Figs. 3 and 4 show the representative real-time NOx concentration signals in NEDC and WLTC modes, which were measured at adjacent positions up- and downstream of the LNT.
Combustion, performance, and selective catalytic reduction of NOx for a diesel engine operated with combined tri fuel (H<inf>2</inf>, CH<inf>4</inf>, and conventional diesel)
2017, EnergyCitation Excerpt :Diesel engines generally emit high nitrogen oxides (NOx) emissions and much higher particulate matter (PM) emissions than spark ignition engines. Among other solutions to reduce both NOx and PM such as reformed EGR [1,2], SCR catalysts [3,4], diesel particulate filters (DPF) [5], and alternative fuels like biofuels and GTL fuels [6,7], combustion of duel fuel or tri fuel concept can also be considered [8–10]. Combined injection of compressed natural gas in conventional diesel engine give lower unburned hydrocarbon and carbon monoxide (CO) emissions, with low output power and thermal efficiency [11,12].
Manganese oxide-based catalysts for low-temperature selective catalytic reduction of NO<inf>x</inf> with NH<inf>3</inf>: A review
2016, Applied Catalysis A: GeneralCitation Excerpt :Therefore, there is a long way before the practical application of MnOx/carbon materials in SCR de-NOx, especially in the low temperature range. For a typical synthesis procedure of practical de-NOx catalysts, catalysts are usually loaded on the surface or mixed into the channel walls of ceramic monolith or parallel passage reactors by wash coating, dip coating, impregnation or extrusion treatment [126–128]. Catalyst loaded onto cordierite honeycomb ceramics with multilayer wash coat performed much better in NH3-SCR reaction compared with the single-phase catalyst [129].
Progress in Adsorptive Removal of Volatile Organic Compounds by Zeolites
2023, Aerosol and Air Quality Research