Alyssa J. R. Hensley

Decomposition of methyl species on a Ni(211) surface: investigations of the electric field influence

Density functional theory calculations are performed to examine how an external electric field can alter the reaction pathways on a stepped Ni(211) surface with regard to the decomposition of methyl species. We compare our results to those previously obtained on a close-packed Ni(111) surface and a bimetallic Au/Ni surface. The structures, adsorption energies, and reaction energy barriers of all methyl species on the Ni(211) surface are identified. The calculated results indicate that the presence of an external electric field not only alters the site preferences for the adsorbates on Ni(211), but also significantly changes the adsorption energies of the CHx species. By comparison with our previous results, this electric field effect is smaller than that on Ni(111). The local electric field value is also found to differ at the various adsorption sites for the CH3 group on Ni(211). From the results, a correlation between the calculated local electric fields, the adsorption energies and effective dipole moments values is investigated. The calculations also show that the stepped surfaces are more reactive for the elementary dissociation reactions of the CHx species as compared to the Ni(111) surface. The final conclusion is that a positive electric field strengthens the adsorption energy of reactant CH3, increases the energy barriers of the decomposition of CHx species and weakens the adsorption energies of C and H. This suggests that the formation of pure C atoms deposits will be impeded by an external positive electric field.

Perspective on Catalytic Hydrodeoxygenation of Biomass Pyrolysis Oils: Essential Roles of Fe-Based Catalysts

Catalytic fast pyrolysis is the most promising approach for biofuel production due to its simple process and versatility to handle lignocellulosic biomass feedstocks with varying and complex compositions. Compared with in situ catalytic fast pyrolysis, ex situ catalytic pyrolysis has the flexibility of optimizing the pyrolysis step and catalytic process individually to improve the quality of pyrolysis oil (stability, oxygen content, acid number, etc.) and to maximize the carbon efficiency in the conversion of biomass to pyrolysis oil. Hydrodeoxygenation is one of the key catalytic functions in ex situ catalytic fast pyrolysis. Recently, Fe-based catalysts have been reported to exhibit superior catalytic properties in the hydrodeoxygenation of model compounds in pyrolysis oil, which potentially makes the ex situ pyrolysis of biomass commercially viable due to the abundance and low cost of Fe. Here, we briefly summarize the recent progress on Fe-based catalysts for the hydrodeoxygenation of biomass, and provide perspectives on how to further improve Fe-based catalysts (activity and stability) for their potential applications in the emerging area of biomass conversion.Graphical Abstract

An atomic-scale view of single-site Pt catalysis for low-temperature CO oxidation

Single-atom catalysts have attracted great attention in recent years due to their high efficiencies and cost savings. However, there is debate concerning the nature of the active site, interaction with the support, and mechanism by which single-atom catalysts operate. Here, using a combined surface science and theory approach, we designed a model system in which we unambiguously show that individual Pt atoms on a well-defined Cu2O film are able to perform CO oxidation at low temperatures. Isotopic labelling studies reveal that oxygen is supplied by the support. Density functional theory rationalizes the reaction mechanism and confirms X-ray photoelectron spectroscopy measurements of the neutral charge state of Pt. Scanning tunnelling microscopy enables visualization of the active site as the reaction progresses, and infrared measurements of the CO stretch frequency are consistent with atomically dispersed Pt atoms. These results serve as a benchmark for characterizing, understanding and designing other single-atom catalysts.Single-atom catalysts are of growing importance, but the nature of their structure and reactivity remains under debate. Here, Sykes and co-workers show that single Pt atoms on a well-defined Cu2O surface are capable of performing low-temperature CO oxidation, and provide data on the binding site and electronic structure of the Pt atoms.