Synergistic Effect of Co/La in Oxygen Vacancy Rich Ternary CoAlLa Layered Double Hydroxide with Enhanced Reductive Sites for Selective Photoreduction of CO2 to CH4

Developing a convenient ternary layered double hydroxide (LDH) semiconductor for highly active photocatalytic reduction is necessary for solving the energy crisis and environmental pollution. In this work, a highly active ternary CoAlLa-LDH was formed through inducing La3+ to enhance coordinatively unsaturated metals centers for development of reductive sites that resulted in improvement of photogenerated charge carrier separation. It was demonstrated that the ratio of cations between the Co/Al/La-LDHs greatly determined the LDH structure for photocatalytic activity toward CO2 reduction. The increase of La content resulted in destruction of LDH structure with lower photoactivity for CO2 reduction. The rate of CO and CH4 evolution in Co2Al1-LDH was about 15.3 and 9.2 mu mol g(cat)(-1) h(-1), much higher than Co3Al1-LDH and Co4Al1-LDH, which indicates that the Co2Al1-LDH among CoAl-LDHs is a promising photocatalyst with high photocatalytic activity in CO2 reduction to CO and CH4. The Co/Al/La molar ratios were optimized to be 2:0.95:0.05 with a production rate of 25.5 mu mol g(cat)(-1) h(-1) and 21.80 mu mol g(cat)(-1) h(-1) for CH4 and CO, respectively. A more interesting finding is that the selectivity of CH4 was raised to 53.93% as compared to 46.10% for CO. Besides, good stability was observed due to the presence of the intact hexagonal nanosheet structure, which was sustained in multiple cycles without obvious deactivation. The highest activity was due to the proper weaving of lanthanum into the framework of LDH. This work demonstrates a facile synthetic method of rationally doping La transition-metal to develop new photocatalyst with remarkable performance in CO2 reduction.