A low-temperature water-gas shift reaction catalyzed by hybrid NiO@NiCr-layered double hydroxides: catalytic property, kinetics and mechanism investigation

摘要

The realization of a high efficiency water gas shift reaction (WGSR) at low temperatures has always been a research hotspot and is difficult to achieve. Based on NiCr layered double hydroxides (NiCr-LDHs), a hybrid NiO@NiCr-LDH was prepared by intercalation and surface complexing. The above materials were applied to WGSR at low temperatures, and the catalytic activity and reaction mechanism of WGSR with NiCr-LDHs and LDHs intercalated with organic metal ligands (NiCr-Ni/SB-LDHs) were compared. It was found that the activity of NiO@NiCr-LDHs was about 4 and 2 times higher than that of NiCr-LDHs and NiCr-Ni/SB-LDHs, respectively. At 150 degrees C, the CO conversion of NiO@NiCr-LDHs is 35.2%, the reaction rate is 19.71 mu mol g(cat)(-1)s(-1), the TOF value is 0.225 s(-1), and the activation energy is 77.4 kJ mol(-1). In addition, the complexing NiO content has a great influence on the activity of NiO@NiCr-LDHs for WGSR. In addition, DFT calculations were used to compare the differences in the performance and catalytic mechanism of different nickel containing LDH catalysts for WGSR. According to the calculated results of relative energy barrier and activation energy, a possible reaction pathway and mechanism are discussed. The results show that compared with NiCr-LDHs and NiCr-Ni/SB-LDHs, NiO@NiCr-LDHs can effectively reduce the activation energy of the H2O dissociation step, which is the rate determining step of WGSR.