ZnAl2O4 Spinel-Supported PdZnβ Catalyst with Parts per Million Pd for Methanol Steam Reforming

Abstract

PdZnβ alloy catalysts have Cu-like properties for a wide range of industrially important reactions, such as methanol synthesis, water–gas shift, and methanol steam reforming, but overcome the major disadvantages inherited by Cu such as sintering and pyrophoric nature. However, high Pd loadings (e.g., >5.0 wt %) are typically required for the synthesis of the PdZnβ alloy, preventing its practical consideration as the replacement of Cu catalysts. Here, we report the synthesis of ZnAl2O4-supported PdZnβ alloy catalysts at extremely low Pd loadings (e.g., 1000 ppm Pd). In particular, a cuboctahedral ZnAl2O4 spinel support with exclusively polar facets provides a strong interaction between Pd and Zn, leading to PdZnβ alloy formation even at low Pd loadings. A 0.1 wt % Pd/ZnAl2O4 catalyst is shown to exhibit superior CO2 selectivity (97%) in the methanol steam reforming reaction, confirming the Cu-like catalytic properties of the PdZnβ alloy even at 1000 ppm Pd. The top-layer Zn species on the exposed polar facets of zinc spinel were found to play a critical role in the preferential formation of the PdZnβ alloy. The advances toward the PdZnβ alloy catalysts with extremely low Pd loadings bring the PdZn alloy catalysts one step closer to a wide range of applications.