First-principles study on the design of nickel based bimetallic catalysts for xylose to xylitol conversion.

A significant challenge for effective biomass utilization and upgrading is catalysis. This research paper focuses on the conversion of xylose into xylitol, a valuable chemical used in the pharmaceutical and food industries. The primary objective is to design more efficient and cost-effective catalysts for this conversion process. The study investigates the use of Ni-bimetallic catalysts by employing a first-principles technique. Catalyst models derived from subsets of Ni (111) surfaces with various transition metals (M = Ti, V, Cr, Fe, Co, and Cu) are examined. The catalyst surfaces are screened based on the rate-determining step (RDS) involved in the conversion of xylose to xylitol, with Ni (111) serving as a reference. Electronic structure calculations are used to analyze the activities of the investigated Ni-bimetallic catalysts relative to the RDS. The results show that certain bimetallic surfaces exhibit significantly lower kinetic barriers compared to the Ni (111) surface. The hydrogenation process when investigated using different transition state paths, reveals that hydrogenation commences at the carbon atom of the carbonyl group of xylose after the ring-opening step. Stability segregation tests demonstrate varying behaviors among the screened catalysts, with Ni (111)/Cr/Ni showing greater stability than Ni (111)/Co. This study sheds light on the theoretical design of catalysts for xylose conversion, providing insights for the development of more efficient and active catalysts for industrial applications. The research highlights the significance of theoretical methodologies in tailoring catalyst surfaces to optimize their performance in biomass upgrading.

Conversion of cyclic xylose into xylitol on Ru, Pt, Pd, Ni, and Rh catalysts: a density functional theory study.

There is currently no theoretical study on the hydrogenation of xylose to xylitol on a catalyst's surface, limiting proper understanding of the reaction mechanisms and the design of effective catalysts. In this study, DFT techniques were used for the first time to investigate the mechanisms of xylose to xylitol conversion on five notable transition metal (TM) surfaces: Ru(0001), Pt(111), Pd(111), Rh(111), and Ni(111). Two transition state (TS) paths were investigated: TS Path A and TS Path B. The TS Path B, which was further subdivided into TS Path B1 and B2, was proposed to be the minimum energy path (MEP) for the reaction process. According to our computational results, the MEP for this reaction begins with the structural rearrangement of cyclic xylose into its acyclic form prior to step-wise hydrogenation. The rate-determining step (RDS) on Ru(0001), Pt(111), Pd(111), and Ni(111) was discovered to be the ring-opening process via C-O bond scission of cyclic xylose. On Rh(111), however, the RDS was found to be the first hydrogenation stage, leading to the hydrogenation intermediate. Furthermore, based on the RDS barrier, our results revealed that the activities of the tested TM surfaces follow the trend: Ru(0001) > Rh(111) ≥ Ni(111) > Pd(111) > Pt(111). This result demonstrates the higher activity of Ru(0001) compared to other surfaces used for xylose hydrogenation. It correlates with experimental trends in relation to Ru(0001) superiority and provides the basis for understanding the theoretical design of economical and more active catalysts for xylitol production.

Hydrogen-Mediated Thin Pt Layer Formation on Ni3N Nanoparticles for the Oxygen Reduction Reaction.

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (Ni3N) nanoparticles were used as earth-abundant metal-based cores to support thin Pt layers. To realize the site-selective formation of Pt layers on the Ni3N core, hydrogen molecules (H2) were used as a mild reducing agent. As H2 oxidation is catalyzed by the surface of Ni3N, the redox reaction between H2 and Pt(IV) in solution was facilitated on the Ni3N surface, which resulted in the selective deposition of Pt on Ni3N. The controlled Pt formation led to a subnanometer (0.5-1 nm)-thick Pt shell on the Ni3N core. By adopting the core-shell structure, higher ORR activity than the commercial Pt/C was achieved. Electrochemical measurements showed that the thin Pt layer on Ni3N nanoparticle exhibits 5 times higher mass activity and specific activity than that of commercial Pt/C. Furthermore, it is expected that the proposed simple wet-chemical method can be utilized to prepare various transition-metal-based core-shell nanocatalysts for a wide range of energy conversion reactions.