Effects of Gas Feed Ratios and Sequence on Ethylene Hydrogenation on Powder Pt Catalyst Studied by Sum Frequency Generation and Mass Spectrometry

• Published in: ACS catalysis 2014-06, Vol.4 (6), p.1964-1971
• Main Authors: Ghosh, Avishek, Hsu, Bryan B, Dougal, Shawn M, Afeworki, Mobae, Stevens, Paul A, Yeganeh, Mohsen S
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/cs500109b

The effects of reactant feed ratios and sequences on ethylene hydrogenation over pellets of Pt powder have been studied using sum frequency generation spectroscopy (SFG) and mass spectrometry (MS) at room temperature and atmospheric pressure. Ethylene hydrogenation is shown to depend not only on the feed ratio but also on the sequence of feed gas injection, which affects the competitive adsorption of reactants (H2, C2H4) and various hydrocarbonaceous intermediates on the catalyst surface. Ethane production was highest when the catalyst was pretreated with hydrogen but diminished with increasing amounts of ethylene. At >2:1 (C2H4/H2) feed ratios, ethane generation was at its lowest, and the SFG spectra of the catalyst surface indicate formation of ethylidyne, di-σ-ethylene, and ethylidene, species that block the Pt surface active sites. We demonstrate that it is possible to partially recover the active sites by flowing H2 through the reactor, although ethane generation was reduced by approximately a factor of 3. Trends in nonresonant SFG (nr-SFG) have been observed to be indicative of H2 adsorption on the Pt surface and are dependent on the sequence of the feed gas injection, as well. We have revealed correlations between nr-SFG and MS ion current of catalytically generated ethane at various pretreatments of the Pt powder surface, thus demonstrating nr-SFG as a sensitive tool to measure catalytic activity of metal surfaces.