ZnAl 2 O 4 Spinel-Supported PdZn β Catalyst with Parts per Million Pd for Methanol Steam Reforming

PdZn β 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 PdZn β alloy, preventing its practical consideration as the replacement of Cu catalysts. Here, we report the synthesis of ZnAl 2 O 4 -supported PdZn β alloy catalysts at extremely low Pd loadings (e.g., 1000 ppm Pd). In particular, a cuboctahedral ZnAl 2 O 4 spinel support with exclusively polar facets provides a strong interaction between Pd and Zn, leading to PdZn β alloy formation even at low Pd loadings. A 0.1 wt % Pd/ZnAl 2 O 4 catalyst is shown to exhibit superior CO 2 selectivity (97%) in the methanol steam reforming reaction, confirming the Cu-like catalytic properties of the PdZn β 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 PdZn β alloy. The advances toward the PdZn β alloy catalysts with extremely low Pd loadings bring the PdZn alloy catalysts one step closer to a wide range of applications.