Rentao Mu

Fast Prediction of CO Binding Energy via the Local Structure Effect on PtCu Alloy Surfaces

CO poisoning is a major problem for Pt-based catalysts in various catalytic processes. Thus, the prediction of CO binding energies over Pt alloy surfaces is fundamentally important to evaluate their CO poisoning tolerance. This article describes the effect of surface and subsurface coordination environments on the CO binding strength over PtCu alloy surfaces by employing density functional theory calculations. We show that the existence of surface Pt neighbors weakens the CO binding strength on Pt, whereas the subsurface Pt neighbors play the opposite role. Crystal orbital Hamilton population analysis suggests a stronger antibonding interaction for the Ptsurface-Ptsubsurface bond than for the Ptsurface-Ptsurface bond, which indicates less stable subsurface Pt atoms that hence generate an activated surface Pt that attracts CO more strongly. On the basis of the calculated CO binding energies, an empirical formula, with Pt-Pt coordination numbers as the variables, has been fitted to achieve a fast prediction of CO binding energy over PtCu alloy surfaces.

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

Carbon dioxide (CO2 ) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu2 O) is a promising catalyst for CO2 reduction as it can convert CO2 into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu2 O remains under debate because of the complex surface structure of Cu2 O under reducing conditions, leading to limited guidance in designing improved Cu2 O catalysts. This paper describes the functionality of surface-bonded hydroxy groups on partially reduced Cu2 O(111) for the CO2 reduction reaction (CO2 RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO2 RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO2 RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination-unsaturated Cu (CuCUS ) sites stabilizes surface-adsorbed COOH*, which is a key intermediate during the CO2 RR. Moreover, the CO2 RR was evaluated over Cu2 O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu2 O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO2 RR and suppress the HER.

Subsurface catalysis-mediated selectivity of dehydrogenation reaction

Subsurface Fe, Co, and Ni can promote the Pt-catalyzed propane dehydrogenation while exposed adversely on the surface. Progress in heterogeneous catalysis is often hampered by the difficulties of constructing active architectures and understanding reaction mechanisms at the molecular level due to the structural complexity of practical catalysts, in particular for multicomponent catalysts. Although surface science experiments and theoretical simulations help understand the detailed reaction mechanisms over model systems, the direct study of the nature of nanoparticle catalysts remains a grand challenge. This paper describes a facile construction of well-defined Pt-skin catalysts modified by different 3d transition metal (3dTM) atoms in subsurface regions. However, on the catalyst containing both surface and subsurface 3dTMs, the selectivity of propane dehydrogenation decreases in the sequences of Pt ~ PtFe > PtCo > PtNi due to the easier C–C cracking on exposed Co and Ni sites. After the exposed 3dTMs were removed completely, the C3H6 selectivity was found to increase markedly in the row Pt < PtNi@Pt < PtCo@Pt < PtFe@Pt, which is in line with the calculated trend of d-band center shifting. The established relationship between reactivity and d-band center shifting illustrates the role of subsurface catalysis in dehydrogenation reaction.

Breaking the scaling relationship via thermally stable Pt/Cu single atom alloys for catalytic dehydrogenation

Noble-metal alloys are widely used as heterogeneous catalysts. However, due to the existence of scaling properties of adsorption energies on transition metal surfaces, the enhancement of catalytic activity is frequently accompanied by side reactions leading to a reduction in selectivity for the target product. Herein, we describe an approach to breaking the scaling relationship for propane dehydrogenation, an industrially important reaction, by assembling single atom alloys (SAAs), to achieve simultaneous enhancement of propylene selectivity and propane conversion. We synthesize γ-alumina-supported platinum/copper SAA catalysts by incipient wetness co-impregnation method with a high copper to platinum ratio. Single platinum atoms dispersed on copper nanoparticles dramatically enhance the desorption of surface-bounded propylene and prohibit its further dehydrogenation, resulting in high propylene selectivity (~90%). Unlike previous reported SAA applications at low temperatures (<400 °C), Pt/Cu SAA shows excellent stability of more than 120 h of operation under atmospheric pressure at 520 °C.Enhancing the catalytic activity of noble-metal alloys is frequently accompanied by side reactions. Here, the authors describe an approach to break the scaling relationship for propane dehydrogenation, by assembling single atom alloys, to achieve simultaneous enhancement of propylene selectivity and propane conversion.

Hydroxyl-Mediated Non-oxidative Propane Dehydrogenation over VO x /γ-Al2O3 Catalysts with Improved Stability

Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt-based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface-bound hydroxyl groups on VOx  / γ-Al2 O3 catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VOx  /Al2 O3 catalyst (V-OH) are produced under H2 pre-reduction, and the catalytic performance for PDH is closely connected to the concentration of V-OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.