Shape Effects of Ceria Nanoparticles on the Water‒Gas Shift Performance of CuOx/CeO2 Catalysts

Abstract

The copper–ceria (CuOx/CeO2) system has been extensively investigated in several catalytic processes, given its distinctive properties and considerable low cost compared to noble metal-based catalysts. The fine-tuning of key parameters, e.g., the particle size and shape of individual counterparts, can significantly affect the physicochemical properties and subsequently the catalytic performance of the binary oxide. To this end, the present work focuses on the morphology effects of ceria nanoparticles, i.e., nanopolyhedra (P), nanocubes (C), and nanorods (R), on the water–gas shift (WGS) performance of CuOx/CeO2 catalysts. Various characterization techniques were employed to unveil the effect of shape on the structural, redox and surface properties. According to the acquired results, the support morphology affects to a different extent the reducibility and mobility of oxygen species, following the trend: R > P > C. This consequently influences copper–ceria interactions and the stabilization of partially reduced copper species (Cu+) through the Cu2+/Cu+ and Ce4+/Ce3+ redox cycles. Regarding the WGS performance, bare ceria supports exhibit no activity, while the addition of copper to the different ceria nanostructures alters significantly this behaviour. The CuOx/CeO2 sample of rod-like morphology demonstrates the best catalytic activity and stability, approaching the thermodynamic equilibrium conversion at 350 °C. The greater abundance in loosely bound oxygen species, oxygen vacancies and highly dispersed Cu+ species can be mainly accounted for its superior catalytic performance.

Approaching C1 Reaction Mechanisms Using Combined Operando and Transient Analysis: A Case Study on Cu/CeO2 Catalysts during the LT-Water–Gas Shift Reaction

“…Cu/CeO 2 catalysts have recently received increasing attention, showing good conversions in low-temperature (LT-)­WGS. ,− According to literature reports, the catalytic activity increases with the Cu loading; , therefore, most studies have focused on highly loaded catalysts. ,, However, normalized to the Cu content, the low-loaded catalysts show higher conversions . Nevertheless, there are no detailed mechanistic studies on the loading dependence of the mechanism itself.…”

“…To this end, theoretical studies have revealed a dependence on the strength of the interaction of Cu with the low-index surface facets, 34,46 which is also reflected in the catalytic activity. 29,[32][33][34]47 For 5 wt % Cu/CeO 2 catalysts, octahedra were found to exhibit the highest WGS activity at ≥200 °C, followed by rods and cubes, by providing the best Cu dispersion, the largest amount of moderately active copper oxide, and the strongest Cu−support interaction. 29 To summarize previous literature findings, the state of copper when supported by ceria strongly depends on the copper loading, and so far a major focus has been placed on highly loaded catalysts.…”

Low-temperature deep oxidation of N,N-dimethylformamide (DMF) over CeCu binary oxides

“…These obtained values are smaller than the pure CeO x 's. 58,59 The lower E g is highly connected with the crystalline phase displacements and oxygen vacancy positions. 60,61 A small E g enables the movement of abundant O Lat at the catalyst's surface, increasing the catalytic activity.…”

Recent Advances on Fine-Tuning Engineering Strategies of CeO2-Based Nanostructured Catalysts Exemplified by CO2 Hydrogenation Processes

“…Hence, particular efforts have been lately devoted to the rational design of CeO 2 -based oxides for WGS by fine-tuning the local surface structure and metal-ceria interactions by means of the aforementioned optimization strategies. In this perspective, the key role of ceria morphology on redox properties and metal-support interactions was disclosed over various CeO 2 -based transition metals [114][115][116]. For instance, the addition of CuO over ceria carriers of different morphology (nanorods (NR), nanocubes (NC), nanopolyhedra (NP)) affects the reducibility to a different extent, following the order NR > NP > NC [114].…”