Herein, lanthanum was incorporated via hydrothermal synthesis into a MCM-41 framework structure with La/Si molar ratios from 0.01 to 0.1. Samples of NiO supported on LaMCM-41 were prepared using the impregnation method. The catalyst performance was evaluated using a fixed bed CO methanation reactor. A Ni/LaMCM-41 catalyst with La/Si = 0.1 shows the best catalytic performance with a CO conversion of almost 100% and a CH4 selectivity of 89.5% at 250 ℃ under a pressure of 1.5 MPa and at an airspeed of 36,000 mL/(g·h). Compared with Ni-La/MCM-41(La/Si = 0.1) and Ni/MCM-41 prepared via the impregnation method, Ni/LaMCM-41(La/Si = 0.1) shows a higher CO conversion and CH4 selectivity.In a 100 h stability test, the Ni/LaMCM-41(La/Si = 0.1) catalyst shows excellent stability; furthermore, the CO conversion is always greater than 98.0%, which is significantly better than the results for Ni/MCM-41.We experimentally demonstrate that elemental La enters the framework of MCM-41. The Ni/LaMCM-41 catalyst performs well because the La reduces the average particle size of the NiO particles and enhances the interaction between NiO and MCM-41; moreover, the introduction of La significantly inhibits the sintering of the catalyst and the formation of carbon deposits.
Nickel-based catalysts represent the most commonly used systems for CO methanation.We have successfully prepared a Ni catalyst system supported on two-dimensional plasma-treated vermiculite(2D-PVMT)with a very low Ni loading(0.5 wt%).The catalyst precursor was subjected to heat treatment via either conventional heat treatment(CHT)or the plasma irradiation method(PIM).The as-obtained CHT-Ni/PVMT and PIM-Ni/PVMT catalysts were characterized with scanning electron microscopy(SEM),energy dispersive X-ray(EDX),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),inductively coupled plasma-atomic emission spectroscopy(ICP-AES)and high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM).Additionally,CHT-NiO/PVMT and PIM-NiO/PVMT catalysts were characterized with hydrogen temperature programmed reduction(H_2-TPR).Compared with CHT-Ni/PVMT,PIM-Ni/PVMT exhibited superior catalytic performance.The plasma treated catalyst PIM-Ni/PVMT achieved a CO conversion of93.5%and a turnover frequency(TOF)of 0.8537 s^(-1),at a temperature of 450°C,a gas hourly space velocity of 6000 ml·g^(-1)·h^(-1),a synthesis gas flow rate of 65 ml·min^(-1),and a pressure of 1.5 MPa.Plasma irradiation may provide a successful strategy for the preparation of catalysts with very low metal loadings which exhibit excellent properties.
