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During reduction in dihydrogen at 873 K, a silica-supported palladium catalyst is initially converted to Pd4Si which further reacts with silicon-containing species to a Pd3Si phase. Such a stepwise phase change suggests that the mechanism of Pd silicide formation involves incorporation of silicon into a palladium phase, not vice versa, as was suggested in our previous work. This transformation has a great effect on catalytic properties of Pd–silica-containing systems in 2,2-dimethylpropane hydroconversion.