Addition of Sodium Additives for Improved Performance of Water-Gas Shift Reaction over Ni-Based Catalysts

Abstract

The effect of Na loading on water-gas shift reaction (WGSR) activity of Ni@TiO _x -XNa (X = 0, 0.5, 1, 2, and 5 wt %) catalysts has been investigated. Herein, we report sodium-modified Ni@TiO _x catalysts (denoted as Ni@TiO _x -XNa) derived from Ni₃Ti₁-layered double hydroxide (Ni₃Ti₁-LDH) precursor. The optimized Ni@TiO _x -1Na catalyst exhibits enhanced catalytic performance toward WGSR at relatively low temperature and reaches an equilibrium CO conversion at 300 °C, which is much superior to those for most of the reported Ni-based catalysts. The H₂-temperature-programmed reduction (H₂-TPR) result demonstrates that the Ni@TiO _x -1Na catalyst has a stronger metal-support interaction (MSI) than the sodium-free Ni@TiO _x catalyst. The presence of stronger MSI significantly facilitates the electron transfer from TiO _x support to the interfacial Ni atoms to modulate the electronic structure of Ni atoms (a sharp increase in Ni^δ- species), inducing the generation of more surface sites (O_v-Ti³⁺) accompanied by more interfacial sites (Ni^δ--O_v-Ti³⁺), revealed by X-ray photoelectron spectroscopy (XPS). The Ni^δ--O_v-Ti³⁺ interfacial sites serve as dual-active sites for WGSR. The increase in the dual-active sites accounts for improvement in the catalytic performance of WGSR. With the tunable Ni-TiO _x interaction, a feasible strategy in creating active sites by adding low-cost sodium addictive has been developed.