Hydrogen migration at restructuring palladium–silver oxide boundaries dramatically enhances reduction rate of silver oxide

Abstract

Heterogeneous catalysts are complex materials with multiple interfaces. A critical proposition in exploiting bifunctionality in alloy catalysts is to achieve surface migration across interfaces separating functionally dissimilar regions. Herein, we demonstrate the enhancement of more than 10 4 in the rate of molecular hydrogen reduction of a silver surface oxide in the presence of palladium oxide compared to pure silver oxide resulting from the transfer of atomic hydrogen from palladium oxide islands onto the surrounding surface formed from oxidation of a palladium-silver alloy. The palladium-silver interface also dynamically restructures during reduction, resulting in silver-palladium intermixing. This study clearly demonstrates the migration of reaction intermediates and catalyst material across surface interfacial boundaries in alloys with a significant effect on surface reactivity, having broad implications for the catalytic function of bimetallic materials.

Evolution of Metastable Structures at Bimetallic Surfaces from Microscopy and Machine-Learning Molecular Dynamics

“…We perform transition state modeling of representative restructuring events for each class, using the Atomic Simulation Environment (ASE) 16,17 with our custom GP calculator. 12 We use the fast inertial relaxation engine (FIRE) algorithm, 18 a damped dynamics method, for all optimizations. We extract raw trajectory fragments of each event with a frame rate of (0.1 ps) −1 .…”

“…To ensure that diverse atomic environments are encountered, all layers are mobile with temperature set at 1100 K via Nosé-Hoover thermostat (40 δt = 0.2 ps coupling). 10,11 The two-and three-body multielement kernel 12 is used as the GP covariance function, with 7.0 and 4.5 Å cutoff for the two-and three-body interactions, respectively. To eliminate redundancy in the training set, the training environments are selected with an active learning protocol that uses the GP Bayesian uncertainty estimates on predicted force components to include only the highest uncertainty atomic environments.…”

Facilitating hydrogen atom migration via a dense phase on palladium islands to a surrounding silver surface

“…Specifically, migration of hydrogen atoms formed on palladium to silver offers a way to enhance selectivity by promoting hydrogenation reactions on silver (31,32). Hydrogen atom migration (often called "spillover") has been demonstrated across a number of metal/metal oxide and metal/metal interfaces (16)(17)(18)(19)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42). However, the migration of hydrogen atoms from palladium to silver is enthalpically unfavorable, making it a difficult process.…”

Ultrafast Metal Oxide Reduction at Pd/PdO2 Interface Enables One-Second Hydrogen Gas Detection Under Ambient Conditions

“…However, to initiate the direct reduction of metal oxides such as PdO, CuO, Cu2O, Ag2O, and NiO by H2 is difficult at room temperature and often requires elevated temperatures to complete. [18][19][20][21][22][23] For example, the apparent activation energy for directly reducing Cu2O by H2 is about 27.4 kcal/mol, and the reduction process took ~180 min to complete, even at 230 °C. Introducing a metal (e.g., Pt, Pd, Ru)/metal oxide interface is a possible solution to accelerating the initial metal oxide reduction kinetics.…”

“…[24][25][26][27][28][29][30][31][32][33][34] Moreover, the metal/metal oxide interface allows facile migration of atomic hydrogen readily dissociated by metals to metal oxides in close proximity (i.e., hydrogen spillover). 21,[35][36][37] The reactive oxygen species and atomic hydrogen react quickly, resulting in the rapid reduction of metal oxide. Thus, tailoring the metal/metal oxide interface offers a unique opportunity to accomplish the challenging 1-s detection of H2 under ambient conditions by rendering ultrafast metal oxide reduction kinetics.…”