Regulating acid sites by transition metals to promote C-H bond cracking ability of Pd catalysts for methane complete combustion performance improvement
Methane is one of the main components of atmospheric pollutants,which is challenging to be eliminated by catalytic oxidation under mild conditions because of its tetrahedral structure stability.In this work,the acidic sites of Pd-based catalysts are modified by introducing transition metals(Cr,Mo,W)to promote the cleavage of C-H bonds and therefore to enhance the catalytic oxidation performance of methane.The oxygen vacancies,acidity and redox property of prepared catalysts are systematically characterized by XRD,Raman,H2-TPR and NH3-TPD techniques.The results show that,the transition metal modification increases the acidic site of Pd catalysts obviously,and the modified PdM catalysts have a higher amount of oxygen vacancies.However,only Mo modified PdMo catalyst exhibits better redox performance,while Cr and W modified PdCr and PdW catalysts show slightly lower redox performance.The results of the methane oxidation reaction confirm that the PdMo catalyst with moderate acidic sites displays excellent performance in the methane oxidation reaction,and its T90 decreases by about 150 ℃,while the PdCr and PdW catalysts with more and less acidic sites show lower methane oxidation activity.The results indicate that the number of acid sites and the redox properties of the catalyst jointly determine the methane oxidation performance.This conclusion provides critical insights for design and preparation of catalysts for complete oxidation of methane at low temperatures.
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