Grafting Ni particles onto SBA-15, and their enhanced performance for CO2 methanation

By a post synthesis method, nickel (Ni) particles could be grafted onto SBA-15 for the first time through chemical bond (-O-Ni-O-Si-O-) formation between silicon (Si) and Ni via oxygen (O) using Ni ammonia (NH3) complex ions (Ni(NH3)(x))(2+) with an NH3/Ni mole ratio of 1-5, which existed as Ni phyllosilicate on the SBA-15 surface, while Ni particles could not be grafted onto SBA-15 in the absence of NH4OH (NH3/Ni mole ratio of 0). An NH3/Ni mole ratio of 2-4 was suitable for grafting conditions, which could give a product with the closest Ni amount to that of raw Ni complex ion solution. The product obtained was named as the Ni-grafted SBA-15 sample. XPS, UV-vis and H-2-TPR analyses demonstrated that a chemical bond was formed between Ni and silicon (Si) via oxygen (O), and no bulk nickel oxides existed in the Ni-grafted SBA-15 sample. The formation of -O-Ni-O-Si-O-was completed via the reaction between hydrolyzate (Ni(OH)(NH3)(x-1))(+) from (Ni(NH3)(x))(2+) and Si-OH (silanol sites) on the SBA-15 surface. The Ni-grafted SBA-15 catalyst suited CO2 methanation, resulting in higher CO2 conversion and methane selectivity than a NiO dispersed SBA-15 catalyst obtained by the conventional post synthesis method. The activation energy for CO2 methanation increased with a decreasing initial Ni amount used. The rate equation for CO2 methanation could be expressed as: r = kC(CO2)(0.64)CH(2)(4.05), where C is the concentration. The Ni-grafted SBA-15 catalyst had high thermal stability for CO2 methanation.