Ethylene hydrogenation catalysis on Pt(111) single-crystal surfaces studied by using mass spectrometry and in situ infrared absorption spectroscopy
Introduction
The hydrogenation of olefins is one of the oldest catalytic processes ever reported, going back as far as 1897 [1], [2], yet it is still quite prominent in many industrial applications, in oil refining and in the food industry to name a few. The basic reaction mechanism for this reaction was proposed many years ago by Horiuti and Polanyi, who suggested that the surface of the metal used as catalyst facilitates the dissociation of molecular H2 into atomic hydrogen so that the adsorbed olefin then can incorporate such H species in a series of stepwise and reversible steps, to first form an alkyl surface intermediate and ultimately the final alkane [3]. This idea still offers the basic framework to explain olefin hydrogenations as well as olefin isomerizations (double-bond migration, cis–trans interconversion [4]), yet it overlooks some subtleties that make the full understanding of the performance of this catalysis elusive [5], [6], [7], [8], [9].
Issues still unresolved in the mechanistic description of the hydrogenation of olefins by transition metals include the sensitivity of the conversion to the structure of the surface and the role of the carbonaceous deposits that form on the surface [6], [8], [10], [11], [12]. Studies with model systems and modern surface-sensitive techniques from many research groups have been directed to answer these questions [7], [9], [13], [14], [15], [16], [17], [18], [19], [20]. Our laboratory in particular has been dedicated to this problem for a number of years, focusing, like many others, on the study of the prototypical case of the hydrogenation of ethylene on Pt(111) single-crystal surfaces [10], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41]. Much progress has been made, but key questions remain unanswered. At present, we are focusing on elucidating the participation of the hydrocarbon species strongly adsorbed on the surface, which in the case of ethylene conversion consist of ethylidyne moieties, in the catalytic conversion [8], [10], and on determining the effect that those may have on the kinetics of molecular hydrogen adsorption and activation.
Toward that end, we have developed an instrument for the operando study of catalytic reactions based on the idea of the so-called high-pressure cell, which is incorporated into the ultrahigh-vacuum (UHV) equipment used for surface preparation and characterization in order to afford great control of the state of that surface before, during, and after catalysis via the ability to directly transfer it between the vacuum and catalytic environments without exposure to the outside atmosphere [42], [43], [44], [45], [46]. We rely on the use of infrared absorption spectroscopy in a single reflection mode (reflection–absorption infrared spectroscopy, or RAIRS [47], [48], [49]) for the in situ characterization of the adsorbed species during reaction, and on the continuous analysis of the gas phase using mass spectrometry to obtain kinetic data [41]. Below we provide some examples of the type of data obtained with this apparatus, discuss its advantages, and indicate the approach to be taken to address the questions mentioned above. We also include some new results from studies using isotope labeling that point to the relative slow nature of hydrogen recombination on the metal surface under catalytic conditions compared to the ethylene hydrogenation and ethylene H-D exchange steps. This is a surprising result, because hydrogen recombination is known to take place readily on clean surfaces [50], [51], [52], [53] and to be key to the behavior of transition metals as catalysts in many hydrogenation processes [6], [54], [55], [56].
Section snippets
Experimental
The experiments were carried out in a two-tier stainless-steel apparatus described in more detail elsewhere [41], [57]. The main chamber is kept under UHV by using a cryogenic pump, and is equipped with a UTI 100C quadrupole mass spectrometer interfaced to a computer to afford the continuous monitoring of the partial pressures of up to 15 masses in a single run. This mass spectrometer is typically used for temperature-programmed desorption (TPD) experiments, but in the work reported here, it
Results
Our ability to follow the kinetics of the catalytic hydrogenation reaction by mass spectrometry (MS) was tested first. Complete mass spectra of the gas mixture present in the high-pressure cell used as the reactor were taken at different stages throughout the conversion to analyze its composition. An example of the data acquired this way is provided in Fig. 1. The mass spectrometry traces evolve over time, indicating the consumption of the reactant (ethylene) and the accumulation of the product
Discussion
Here we report the results from some of our operando studies on the hydrogenation of ethylene promoted by a Pt(111) single-crystal surface that combine the continuous determination of the gas composition using mass spectrometry with the simultaneous RAIRS characterization of the surface intermediates. Much of what we have seen in these studies has been reported before and is therefore not worth discussing in great detail here. For instance, the RAIRS data show the presence of ethylidyne species
Conclusions
In this report, we discuss the use of an instrument combining typical UHV techniques and a so-called high-pressure cell for the study of olefin hydrogenation reactions catalyzed by a Pt(111) single-crystal surface. Our equipment is in many ways similar to that of others, except that we have chosen to use mass spectrometry instead of gas chromatography for the detection and quantitation of the gas mixture during reaction, and reflection–absorption infrared spectroscopy (RAIRS) for the
Acknowledgments
Funds for this project were provided by the US National Science Foundation, Division of Chemistry, under Contract No. CHE-1359668.
References (97)
Surf. Sci.
(1989)- et al.
Surf. Sci.
(1992) J. Mol. Catal.
(1994)- et al.
Surf. Sci.
(1995) - et al.
J. Catal.
(1996) - et al.
Surf. Sci.
(1996) - et al.
J. Catal.
(1998) - et al.
Surf. Sci.
(2000) - et al.
Surf. Sci.
(2000) Appl. Catal. A
(2002)
Adv. Catal.
Surf. Sci. Rep.
Surf. Sci. Rep.
Surf. Sci. Rep.
J. Electron Spectrosc. Relat. Phenom.
Surf. Sci.
J. Catal.
Surf. Sci.
Surf. Sci. Rep.
Appl. Surf. Sci.
Surf. Sci. Lett.
Surf. Sci.
J. Catal.
J. Catal.
J. Catal.
Surf. Sci.
Surf. Sci.
J. Mol. Catal. A Chem.
Seances Acad. Sci.
Encyclopedia of Inorganic and Bioinorganic Chemistry
Trans. Faraday Soc.
Nat. Mater.
J. Phys. Chem. B
Metal-Catalysed Reactions of Hydrocarbons
J. Phys. Chem. B
Phys. Chem. Chem. Phys.
Nat. Commun.
Langmuir
Top. Catal.
ACS Catal.
J. Am. Chem. Soc.
J. Am. Chem. Soc.
J. Am. Chem. Soc.
J. Am. Chem. Soc.
J. Phys. Chem. B
J. Phys. Chem. C
Catal. Lett.
J. Phys. Chem. B
Cited by (20)
Adsorption, thermal conversion, and catalytic hydrogenation of acrolein on Cu surfaces
2022, Journal of CatalysisCitation Excerpt :Acrolein was purchased from Aldrich (>90 purity), purified in situ by performing several freeze–pumpthaw cycles, and introduced into either the UHV chambers or the catalytic batch reactor using its vapor (and leak valves in the UHV cases). The raw TPD and kinetic data were deconvoluted and calibrated using a protocol developed in our laboratory to convert mass spectrometer signals into partial pressures for the different reactants and products [55–57]. The signals for 56, 57, 58, and either 59 or 31 amu (59 amu for the TPD, 31 amu for the catalytic kinetics) were selected for these calculations, as they are important peaks in the mass spectra of acrolein (2-propenal), allyl alcohol (2-propenol), propanal, and 1-propanol, respectively; these are the main reactants and products expected from acrolein hydrogenation.
Adsorption of SF<inf>6</inf> decomposition gases (H<inf>2</inf>S, SO<inf>2</inf>, SOF<inf>2</inf> and SO<inf>2</inf>F<inf>2</inf>) on Sc-doped MoS<inf>2</inf> surface: A DFT study
2021, Applied Surface ScienceCitation Excerpt :Among the method of detecting the decomposed gases of SF6, the tube detection method, gas chromatography and infrared absorption spectrometry all have certain limitations. More importantly, the above techniques are all offline and cannot monitor GIS in real-time [7-9]. In recent years, the semiconductor sensor method has been widely used to detect SF6 decomposition gases due to its low cost, high sensitivity and online monitoring.
Measurements of C<inf>2</inf>H<inf>4</inf> transitions near 1.625 μm and C<inf>2</inf>H<inf>4</inf> concentrations using the WM-DAS method
2019, Vibrational SpectroscopyCitation Excerpt :Real-time measurements of C2H4 concentrations for pulsed detonation engines (PDEs) operating on oxygen and air used the spectral absorption near 3.39 μm [27,28]. In addition, reflection-absorption infrared spectroscopy of ethylene was also used to study the adsorption of ethylene on hydrogen-covered Pd(1 1 1) [29,30] and the catalytic hydrogenation of ethylene promoted by a Pt(1 1 1) [31] single crystal. Although the mid-infrared absorption is one or two orders of magnitude stronger than that in the near-infrared region, the light intensity can easily be saturated in practical environments with a long light path.
Infrared spectroscopy of coordination and solvation in Cu<sup>+</sup>(C<inf>2</inf>H<inf>4</inf>)<inf>n</inf> (n = 1–9) complexes
2019, International Journal of Mass SpectrometryCitation Excerpt :Metal cation-ethylene complexes serve as convenient models to study the fundamental details of metal-olefin interactions. These interactions are particularly relevant to catalysis, in processes such as Ziegler-Natta polymerization, endothermic combustion, and platinum or iridium catalyzed hydrogenation [1–5]. Recent developments in the field of single site catalysis have employed metal complexes, clusters, and atoms distributed on surfaces and in porous materials such as metal-organic frameworks and zeolites [6–10].
Surface science approach to Pt/carbon model catalysts: XPS, STM and microreactor studies
2018, Applied Surface ScienceCitation Excerpt :Here, we report first results of preparing Pt/HOPG model catalysts, their characterization by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) in UHV, and their catalytic testing for ethylene hydrogenation in a flow microreactor at atmospheric pressure. Ethylene hydrogenation to ethane is a benchmark reaction for model catalysts and has been repeatedly examined [21,37–42]. Two different model catalysts were prepared, with Pt particles of 2.0 and 3.6 nm mean size.
Kinetic aspects of operando studies: state-of-the-art and unexplored possibilities
2017, Mendeleev Communications
C bond. Thermal activation leads to early dissociation and dehydrogenation to produce acetylene and carbon monoxide below 160 K, and later to the production of ketene (220 K) and propene (260 K). Under vacuum hydrogenation with H2 is not possible, but upon predosing of the surface with atomic H all the possible hydrogenation products, namely, propanal, 1-propanol, and allyl alcohol, were detected in TPD experiments, at 162, 190, and 210 K, respectively. Finally, catalytic hydrogenation under atmospheric pressures is slow and only produces propanal, at turnover frequencies below 0.2 s−1.
H stretching region (2600–3400 cm−1). Argon tagging is employed to study the spectra of the n = 1–3 complexes. Spectra of complexes containing four to nine ligands are measured by the elimination of ethylene. Density functional theory calculations are carried out in support of the experimental spectroscopy. The symmetric C