Mechanism Investigations on Water Gas Shift Reaction over Cu(111), Cu(100), and Cu(211) Surfaces

Cu-based catalysts are commonly applied in low-temperature water gas shift (WGS) reactions, owing to their low cost and high catalytic activity. The influence of different Cu surfaces on catalytic activity and mechanism over the WGS reaction remains unclear. In this work, the effect of different structures of surfaces on the WGS mechanism is studied using density functional theory (DFT). Three surface terminations (Cu(100), Cu(111), and Cu(211)) of Cu are considered, and the coordination number (CN) of the active Cu site is in the range from 7 to 9. The most stable surface is Cu(211). Then, d-band center values are calculated, which decrease in the following sequence: Cu(211) > Cu(100) > Cu(111). This shows that d-band center values decrease with increasing coordination number. The increase in the centers of the d-band leads to an increase in the adsorption strength of CO and H₂O adsorbates, which is in line with the theory of the d-band center. In addition, the further calculated mechanism for WGS reaction over three different Cu surfaces illustrates that the carboxyl path is the most favorable mechanism, and the rate-determining step is H₂O dissociation. Cu(211) shows excellent WGS catalytic performance, better than the Cu(100) and Cu(111) surfaces. This work provides theoretical insights into the rational design of highly active Cu-based catalysts toward WGS reaction.

The Effect of CeO2 Preparation Method on the Carbon Pathways in the Dry Reforming of Methane on Ni/CeO2 Studied by Transient Techniques

The present work discusses the effect of CeO2 synthesis method (thermal decomposition (TD), precipitation (PT), hydrothermal (HT), and sol-gel (SG)) on the carbon pathways of dry reforming of methane with carbon dioxide (DRM) applied at 750 °C over 5 wt% Ni/CeO2. In particular, specific transient and isotopic experiments (use of 13CO, 13CO2, and 18O2) were designed and conducted in an attempt at providing insights about the effect of support’s preparation method on the concentration (mg gcat−1), reactivity towards oxygen, and transient evolution rates (μmol gcat−1 s−1) of the inactive carbon formed under (i) CH4/He (methane decomposition), (ii) CO/He (reverse Boudouard reaction), and (iii) the copresence of the two (CH4/CO/He, use of 13CO). Moreover, important information regarding the relative contribution of CH4 and CO2 activation routes towards carbon formation under DRM reaction conditions was derived by using isotopically labelled 13CO2 in the feed gas stream. Of interest was also the amount, and the transient rate, of carbon removal via the participation of support’s labile active oxygen species.