The Cu–ZnO synergy in methanol synthesis from CO2, Part 1: Origin of active site explained by experimental studies and a sphere contact quantification model on Cu + ZnO mechanical mixtures

The Cu–ZnO synergy in methanol synthesis from CO2, Part 2: Origin of the methanol and CO selectivities explained by experimental studies and a sphere contact quantification model in randomly packed binary mixtures on Cu–ZnO coprecipitate catalysts

“…Recently, we reported [14] that the so-called synergy originates from the contacts between Cu and ZnO created during the reduction step of the catalyst. The formed active phase for methanol production was identified to be ZnO x catalytic sites.…”

A one-step Cu/ZnO quasi-homogeneous catalyst for DME production from syn-gas

“…34 Regardless of the precise nature of the active site or sites, it is now widely accepted that a Cu/ZnO interface is required to form the active site and thus, strategies to maximise the interface are important to improve activity. 34,53 The extent of Cu interacting with ZnO can be estimated by comparing the activity per mass of Cu for the catalysts. Using such an approach for the hybrid catalysts, shows a linear correlation between the activity per mass of Cu and the Zn/(Cu+Zn) ratio.…”

Revisiting Catalyst Structure and Mechanism in Methanol Synthesis

“…ZnO (< 673 K) and Cu by themselves have a low activity for methanol synthesis. Once paired, the activity increases by several orders of magnitude [7]. Recent studies suggested that distorted (or stepped) metallic Cu surface is active.…”

“…To explain these synergistic effects, three main theories have been proposed: (1) active site creation through Cu/Zn alloys, (2) morphological synergies, and (3) a hydrogen reservoir formed on ZnO through hydrogen spillover, which efficiently promotes CO 2 conversion when Cu and ZnO surfaces are adjacent [7]. All three theories can be explained through Zn migration creating a bronze-like Cu x Zn (1-x) O y active phase which occurs solely on the boundary between Cu and ZnO particles [10].…”

“…All three theories can be explained through Zn migration creating a bronze-like Cu x Zn (1-x) O y active phase which occurs solely on the boundary between Cu and ZnO particles [10]. The mechanism that best characterizes this migration is the Kirkendall effect, in which differing diffusion rates between two metallic surfaces causes boundary layer movement between these surfaces, thereby leading to a more uniformly active catalyst and preventing cluster formation of Cu or ZnO as illustrated in Figure 1 [7]. The bronze-like active phase of Cu x Zn (1-x) O y has been effectively reproduced on mechanical mixtures, coprecipitates and core-shell morphologies.…”