Oxidative steam reforming of ethanol over M x La2- x Ce1.8Ru0.2O7- δ (M = Mg, Ca) catalysts: effect of alkaline earth metal substitution and support on stability and activity

Ho-Chen Hsieh; Ping-Wen Tsai; Yuan-Chia Chang; Sheng-Feng Weng; Hwo-Shuenn Sheu; Yu-Chun Chuang; Chi-Shen Lee

doi:10.1039/c9ra08385e

Oxidative steam reforming of ethanol over M _x La_{2- x} Ce_1.8Ru_0.2O_{7- δ} (M = Mg, Ca) catalysts: effect of alkaline earth metal substitution and support on stability and activity

RSC Adv. 2019 Dec 5;9(68):39932-39944. doi: 10.1039/c9ra08385e. eCollection 2019 Dec 2.

Authors

Ho-Chen Hsieh^{1

2}, Ping-Wen Tsai¹, Yuan-Chia Chang¹, Sheng-Feng Weng¹, Hwo-Shuenn Sheu^{2

3}, Yu-Chun Chuang³, Chi-Shen Lee^{1

4}

Affiliations

¹ Department of Applied Chemistry, National Chiao Tung University 1001 University Rd. Hsinchu 30010 Taiwan chishen@mail.nctu.edu.tw.
² Graduate Degree Program of Science and Technology of Accelerator Light Source, National Chiao Tung University Hsinchu 30010 Taiwan.
³ National Synchrotron Radiation Research Center Hsinchu 30010 Taiwan.
⁴ Center for Emergent Functional Matter Science, National Chiao Tung University Hsinchu 30010 Taiwan.

Abstract

Alkaline earth metal substitutions on the A-site of pyrochlore oxide M _x La_2-x Ce_1.8Ru_0.2O_7-δ (M = Mg, Ca) were studied as catalyst materials for oxidative/autothermal steam reforming of ethanol (OSRE/ATR). The as-prepared oxides were synthesized by a combustion method and characterized using powder X-ray diffraction (PXRD), and X-ray photoelectron and absorption spectroscopy (XPS and XAS). PXRD Rietveld analysis and elemental analysis (ICP-AES) support the formation of a pyrochlore-type structure (space group Fd3̄m) with a distorted coordination environment. The substitution of Mg²⁺ and Ca²⁺ ions affects the oxidation states of Ce^4+/3+ and Ru ⁿ⁺ ions and creates oxygen vacancies, which leads to enhanced catalytic activity and reduced ethylene selectivity. A long-term stability test showed optimized catalysts Mg_0.3La_1.7Ce_1.8Ru_0.2O_7-δ and Ca_0.2La_1.8Ce_1.8Ru_0.2O_7-δ with S _H₂ = 101(1)% and S _H₂ = 91(2)% under OSRE conditions. The initial operation temperatures were lower than that of the unsubstituted catalyst La₂Ce_1.8Ru_0.2O_7-δ . Catalysts supported on La₂Zr₂O₇ showed stable OSRE/ATR performance and low carbon deposition compared to catalysts supported on Al₂O₃. We ascribe the enhanced activity to well-dispersed alkaline earth metal and Ru ions in a solid solution structure, synergistic effects of (Mg, Ca)²⁺/Ce^3+/4+/Ru ⁿ⁺ ions, and a strong catalyst-support interaction that optimized the ethanol conversion and hydrogen production.