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 Niδ- species), inducing the generation of more surface sites (Ov-Ti3+) accompanied by more interfacial sites (Niδ--Ov-Ti3+), revealed by X-ray photoelectron spectroscopy (XPS). The Niδ--Ov-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.