CuO-CeO2 nanocomposite catalysts produced by mechanochemical synthesis

Ch Borchers,A V Leonov,E Z Kurmaev,A I Kukharenko,G A Vorobjeva,I S Zhidkov,A A Firsova,M L Martin,O S Morozova,S O Cholakh

doi:10.1063/1.5109067

Abstract

Mechanochemical synthesis based on ball-milling of individual oxides was applied as a one-step preparation technique for CuO-CeO2 catalyst for preferential CO oxidation in H2 excess. The mechanical energy dose transferred to the original powder mixture determines both the catalyst composition and activity. It is found that after 90 min of milling (corresponding to a dose of 372 kJ mol–1), a mixture of 10 wt.% CuO-CeO2 powder exhibits a CO conversion of 97% at 423 K. Four active oxygen states, which are not observed in case of pure CeO2, were detected in the nanocomposite lattice and attributed to the presence of Cu in surface sites as well as in subsurface bulk sites of CeO2, in nearest neighbor and next nearest neighbor positions. Correspondingly, oxidation of CO to CO2 was found to occur in a two-stage process with Tmax = 395/460 K, and oxidation of H2 to H2O likewise in a four-stage process with Tmax = 426/448/468/516 K. The milled powder consists of CeO2 crystallites sized 8–10 nm agglomerated to somewhat larger aggregates, with CuO dispersed on the surface of the CeO2 crystallites, and to a lesser extent present as Cu2O.

Highlights

Synergy in CuO and CeO2 redox properties is proven by temperature programmed scitation.org/journal/adv reduction (TPR) experiments confirming a significant decrease in the reduction temperature, as compared to individual oxides (Ren et al, 2017; Liu and Flytzani-Stephanopoulos, 1996; Qi and Flytzani-Stephanopoulos, 2004; and Polster et al, 2009)
We studied the catalytic behavior of a Cu-CeO2 nanocomposite produced by mechanochemical synthesis (Borchers et al, 2016)
Just as in case of the Cu-CeO2 nanocomposite, ball milling is an effective and cheap method to produce CuO-CeO2 nanocomposites suitable for preferential oxidation of CO in the presence of H2; nanocomposites prepared by this simple technique are comparable in catalytic properties with catalysts synthesized by different traditional preparation methods such as wet impregnation, co-precipitation, sol-gel method, urea-nitrate combustion and hydrothermal methods (Yang et al, 2009; Prasad and Rattan, 2010; Maciel et al, 2012; and Cecilia et al, 2017)

Summary

Introduction

CuO-CeO2 catalysts are widely used in commercially and ecologically important processes, especially in CO-preferential oxidation (CO-PROX) - low temperature oxidation of CO in excess hydrogen (Li et al, 2010; Maciel et al, 2011; Martínez-Arias et al, 2013; Wongkaew et al, 2013; Galvita et al, 2014; Monte et al, 2014; Yao et al, 2014; Ding et al, 2018; Hossain et al, 2018; Jing et al, 2019; and Zhao et al, 2019). Synergy in CuO and CeO2 redox properties is proven by temperature programmed scitation.org/journal/adv reduction (TPR) experiments confirming a significant decrease in the reduction temperature, as compared to individual oxides (Ren et al, 2017; Liu and Flytzani-Stephanopoulos, 1996; Qi and Flytzani-Stephanopoulos, 2004; and Polster et al, 2009). Both are indicative of a new CuO-CeO2 composition being formed: CuO nanoinclusions in CeO2 or CuxCe1-xOy solid solutions. The most commonly used techniques are wet impregnation, co-precipitation, sol-gel method, urea-nitrate combustion and hydrothermal methods (Yang et al, 2009; Prasad and Rattan, 2010 and references therein; Maciel et al, 2012; and Cecilia et al, 2017)

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Discussion

Conclusion