Reforming Methane with CO2 over Hierarchical Porous Silica-Supported Nickel Catalysts Modified with Lanthanum Oxide

Abstract

Hierarchical porous silica-supported nickel catalysts modified with different amounts of lanthanum (La) were synthesized via “one-pot” method using cetyltrimethylammonium bromide as template, urea as precipitant, and tetraethyl orthosilicate as silica source. Their catalytic performances were evaluated in dry reforming with methane under different conditions (La loading, reaction temperature, and time on stream). The synthesized and spent catalysts were extensively characterized by ICP, physisorption, chemisorption, XRD, TPR, XPS, HAADF-TEM, TPH, Raman’s spectroscopy, and TG analysis. The impact of lanthanum amount on the catalytic performance, sintering, and carbon deposition was discussed. Compared to unmodified catalyst, La promoter induced the nickel nanoparticles with larger crystallite sizes and weakened the metal-support interaction as well as the formation of 1 : 1 nickel-phyllosilicate, leading to the metal sintering increasing in the order Ni1.5La/SiO2 < Ni3.0La/SiO2 < Ni4.5La/SiO2. The modified catalysts exhibited better carbon resistance, which was significantly enhanced with increasing La content. Despite this, the stability increased following the sequence of Ni3.0La/SiO2 < Ni4.5La/SiO2 < Ni1.5La/SiO2. Ni1.5La/SiO2 displayed the best stability at 750°C within 10 h stability test, with CH4 conversion dropping from 61.3 to 58.0%. The deactivation reason for Ni1.5La/SiO2 was mainly the carbon deposition, while that for Ni3.0La/SiO2 and Ni4.5La/SiO2 was the metal sintering. These results emphasized that the activity and stability in the NiLa/SiO2 catalysts for the dry reforming of methane depended on two important factors, the metal-support interaction and the particles size of nickel, providing the necessity and sufficiency to balance two attributes.