Following the structure of copper-zinc-alumina across the pressure gap in carbon dioxide hydrogenation

TLDR: In this paper, the state and evolution of the catalyst is defined by its environment, and the structure of the catalysts shows a strong pressure dependence, especially below 1 bar, which is a general problem in catalysis.

Abstract: Copper-zinc-alumina catalysts are used industrially for methanol synthesis from feedstock containing carbon monoxide and carbon dioxide. The high performance of the catalyst stems from synergies that develop between its components. This important catalytic system has been investigated with a myriad of approaches, however, no comprehensive agreement on the fundamental source of its high activity has been reached. One potential source of disagreement is the considerable variation in pressure used in studies to understand a process that is performed industrially at pressures above 20 bar. Here, by systematically studying the catalyst state during temperature-programmed reduction and under carbon dioxide hydrogenation with in situ and operando X-ray absorption spectroscopy over four orders of magnitude in pressure, we show how the state and evolution of the catalyst is defined by its environment. The structure of the catalyst shows a strong pressure dependence, especially below 1 bar. As pressure gaps are a general problem in catalysis, these observations have wide-ranging ramifications. Copper-zinc-alumina is used in industry to catalyse the synthesis of methanol from CO2, but many aspects of its high performance remain elusive. Now, by using in situ and operando techniques over four orders of magnitude in pressure, the authors show how the catalyst structure and kinetics change with the applied conditions.