HCOOH Decomposition on Sub-Nanometer Pd6 Cluster Catalysts: The Effect of Defective Boron Nitride Supports Through First Principles

Abstract

The catalytic properties of a hexagonal boron nitride- (h-BN) supported Pd6 sub-nanometer cluster in the context of formic acid (HCOOH) decomposition were studied by means of periodic Density Functional Theory (DFT) calculations. The effect of support defectivity – boron (h-BvN) and nitrogen (h-BNv) monovacancies – on the competition between the formate (HCOO)- and carboxyl (COOH)-mediated decomposition pathways was analyzed. Defects are responsible for charge-transfer leading to a positively or negatively charged cluster, and open new reactive channels in which vacancy-mediated dehydrogenation pathways can occur. Pd6 cluster reconstructions, induced by the adsorption of reaction intermediates and by the presence of monovacancies in the support, greatly stabilize the formation of CO from COOH, which could drastically decrease the selectivity towards hydrogen production. A simplified descriptor-based analysis, based on selected thermochemical quantities calculated on charged cluster models, suggests that Pd6 sub-nanometer clusters supported on pristine h-BN and h-BNv can be more selective than Pd6 supported on defective h-BvN towards HCOOH dehydrogenation.