Engineering the ZrO₂–Pd Interface for Selective CO₂Hydrogenation by Overcoating an Atomically Dispersed Pd Precatalyst

Abstract

Tailoring the interfacial sites between metals and metal oxides can be an essential tool in designing heterogeneous catalysts. These interfacial sites play a vital role in many renewable applications, for instance, catalytic CO2 reduction. Postsynthesis deposition of metal oxide on supported metal catalysts can not only create such interfacial sites but also prevent particle sintering at high temperature. Here, we report a sol–gel-based strategy to synthesize an atomically dispersed “precatalyst”. In contrast to the deposition on catalysts containing preformed nanoparticles, overcoating this material before reductive treatment can inhibit particle growth during thermal activation steps, yielding highly accessible, sintering-resistant Pd clusters that are less than 2 nm in diameter. This synthetic approach allows us to engineer interfacial sites while maintaining high metal accessibility, which was difficult to achieve in previous overcoated materials. Notably, engineering the Pd–ZrO2 interface into an inverted interface with an amorphous ZrO2 overcoat might facilitate a C–O cleavage route instead of a mechanism containing a bicarbonate intermediate during CO2 hydrogenation. We also observed that carbon deposition occurring on methanation sites could be a key factor for improving CO selectivity. Alteration of the reaction pathway, along with the deactivation of certain sites, led to 100% CO selectivity on the ZrO2@Pd/ZrO2 catalyst. This work demonstrated that overcoated materials could represent a promising class of heterogeneous catalysts for selective CO2 conversion over noble metals, which have higher rates and thermal stability compared to state-of-the-art Cu-based catalysts.

Steering CO 2 hydrogenation toward C–C coupling to hydrocarbons using porous organic polymer/metal interfaces

“…All the corresponding Ru/oxide catalysts produced predominantly methane as product ( Fig. 5 H ), in agreement with previous reports ( 24 , 30 , 32 , 34 , 50 ), with Ru/ZrO 2 being the only exception and showing prominent RWGS selectivity of 78% possibly due to either strong metal support interactions ( 51 ) or Ru redispersion ( 52 ). Nevertheless, in all cases it was found that IPOP encapsulation significantly promoted CO production through RWGS pathway and, more importantly, much increased C 2+ hydrocarbon selectivity.…”

Insights into the Influence of ZrO2 Crystal Structures on Methyl Laurate Hydrogenation over Co/ZrO2 Catalysts

“…From previous findings, the metal site in cooperation with the oxygen vacancy site of ZrO 2 was responsible for the adsorption and activation of oxygenated molecules. 36,61,62 According to XPS (Tables S5 and S6) and OSC results, Co/ZR3 exhibited the highest concentration of oxygen vacancies on the catalyst surface, which seemed to verify the fact that the presence of oxygen vacancy on the ZrO 2 support contributed to substrate activation.…”

Co Single Atoms in ZrO2 with Inherent Oxygen Vacancies for Selective Hydrogenation of CO2 to CO

“…For example, in a Ru/CeO 2 single-atom catalyst, CO was stabilized at the interface and methane was produced by its successive hydrogenation . Therefore, along with the isolation of metal atom sites, it is important to understand the role of interfacial site to control the activity and selectivity of catalysts. − …”