Theoretical understandings on the unusual selectivity of 1,3-Butadiene hydrogenation to butenes over gold catalysts

Comparative Study of Pd-Ni Bimetallic Catalysts Supported on UiO-66 and UiO-66-NH2 in Selective 1,3-Butadiene Hydrogenation

Selective hydrogenation of 1,3-butadiene (BD) is regarded as the most promising route for removing BD from butene streams. Bimetallic Pd-Ni catalysts with changed Pd/Ni molar ratios and monometallic Pd catalysts were synthesized using two differently structured metal-organic framework supports: UiO-66 and UiO-66-NH₂. The effects of the structure of support and the molar ratio of Pd/Ni on the catalytic property of selective BD hydrogenation were studied. The Pd-Ni bimetallic supported catalysts, PdNi/UiO-66 (1:1) and PdNi/UiO-66-NH₂ (1:1), exhibited fine catalytic property at low temperature. Compared with UiO-66, UiO-66-NH₂ with a certain number of alkaline sites could reduce the catalytic activity for the BD hydrogenation reaction. However, the alkaline environment of UiO-66-NH₂ is helpful to improve the butene selectivity. PdNi/UiO-66-NH₂ (1:1) catalyst presented better stability than PdNi/UiO-66 (1:1) under the reaction conditions, caused by the strong interaction between the -NH₂ groups of UiO-66-NH₂ and PdNi NPs. Moreover, the PdNi/UiO-66-NH₂ (1:1) catalyst presented good reproducibility in the hydrogenation of BD. These findings afford a beneficial guidance for the design and preparation of efficient catalysts for selective BD hydrogenation.

Addressing the uncertainty of DFT-determined hydrogenation mechanisms over coinage metal surfaces

Density functional theory (DFT) has been considered as a powerful tool for the identification of reaction mechanisms. However, it is still unclear whether the error of DFT calculations would lead to mis-identification of mechanisms. Here, taking the hydrogenation of acetylene and 1,3-butadiene as model reactions and employing a well-trained Bayesian error estimation functional with van der Waals correlation (BEEF-vdW), we try to estimate the error of DFT calculation results statistically, and therefore predict the reliability of the hydrogenation mechanisms identified. With an ensemble of 2000 functionals obtained around the BEEF-vdW functional as well as a descriptor developed to represent the possibility of different mechanisms, we found that the non-Horiuti-Polanyi mechanism is preferred on Ag(211) and Au(211), while the Horiuti-Polanyi mechanism is dominant on Cu(211). We further discovered that the descriptor is linearly correlated with the adsorption energies of reaction intermediates during acetylene and butadiene hydrogenation, and the hydrogenation of strongly adsorbed species are more likely to follow the Horiuti-Polanyi mechanism. We found the probability of following the non-HP mechanism obeys the order Cu(211) < Au(211) < Ag(211). Our work gives a more comprehensive explanation for the mechanisms of coinage metal catalyzed hydrogenation reactions, and also provides more theoretical insights into the development of new high-performance catalysts for selective hydrogenation reactions.

Ethanol steam reforming on Rh: microkinetic analyses on the complex reaction network

Reaction networks were generated for ethanol steam reforming to CO and CO2. After the pruning of the networks, the preferred reaction pathways of the CO and CO2 production on Rh(111) were identified and detailed kinetic information was analyzed.