Ethanol Dry Reforming for Hydrogen-Rich Syngas Production over Cu-Promoted Ni/Al2O3–ZrO2 Catalysts

Abstract

Development of stable Ni-based catalysts with high resistance to sintering and carbon deposition is a challenge in the catalytic ethanol dry reforming (EDR) process. An effective and practical strategy is to introduce a second metal to obtain Ni-based bimetallic catalysts. In this study, bimetallic Cu–Ni nanoparticles supported on Al–Zr–Ce (ACZ) complex oxides were successfully developed as a multifunctional catalyst for syngas production via EDR and were compared with monometallic Ni and Cu catalysts supported on ACZ oxides. The addition of a small amount of copper (1%) to the catalyst resulted in the formation of a Cu–Ni alloy with crystallite sizes ranging from 10 to 30 nm, exhibiting a high metal–support interaction and resistance to sintering. However, a high Cu content limited the activity of the catalysts due to side reactions of ethanol decomposition, which led to catalyst deactivation. The catalyst 1Cu–9Ni/50ACZ exhibited the highest H₂ and CO yields (78% and 70%, respectively, at T = 750 °C) at H₂/CO = 1.1. The addition of Cu enhanced the H₂/CO ratio by shifting the water–gas shift (WGS) reaction pathway and increasing the reducibility and dispersibility of Ni, which is attributed to the formation of a Cu–Ni alloy. The Cu–Ni alloy is active in the WGS reaction and has a synergistic effect with Ni in dehydration and dehydrogenation of ethanol, which affects the product distribution. Furthermore, copper plays a role in the reduction of carbide forms of nickel, which are precursors of graphitized coke. The support composition was also found to have a significant effect on the activity and stability of the bimetallic catalysts. It was demonstrated that the Al/Zr ratio in the support enables tuning the crystallite size of the active phase, which affects the surface concentrations of nickel and copper and their ratio and determines the ratio of reactive oxygen species that contribute to the gasification of the formed coke. This work provides a strategy to design highly selective catalysts with functional metal sites for hydrogen or syngas production with a regulated H₂/CO ratio.