Facile, template-free synthesis of macroporous SiO2 as catalyst support towards highly enhanced catalytic performance for soot combustion

•Macroporous SiO2 is prepared without template via the adjustment of the sol.•The gentle Brownian motion benefits the growth of silica colloidal particles.•The inter-particle distance could stretch the network structure of SiO2.•The electric double layer restrains the agglomeration of colloidal particles.•Macroporous SiO2 supported K2O catalysts show superior soot oxidation activity.