The effect of the calcium dopant on the activity and selectivity of gold catalysts supported on SBA-15 and Nb-containing SBA-15 in methanol oxidation

Abstract

Gold catalysts based on SBA-15 and niobium-containing SBA-15 (NbSBA-15, to which niobium was introduced in one pot synthesis, and Nb₂O₅/SBA-15 prepared by post-synthesis impregnation of SBA-15) were doped with calcium species introduced before Au loading and were tested in gas-phase methanol oxidation with oxygen at different temperatures. Moreover, gold was loaded on the support prepared by the simultaneous post-synthesis modification of SBA-15 with a mixture of niobium(V) oxide and calcium oxide (Au/CaNbO_x/SBA-15 sample). The structural/textural parameters (XRD, N₂ adsorption/desorption), concentration of the surface species (XPS), as well as the surface acid–base properties (test reaction-2-propanol decomposition) of all catalysts were studied after the activation of materials in argon flow at 623 K. Moreover, the oxidation states and concentration of catalyst components were analyzed after methanol oxidation. FTIR study combined with methanol and oxygen adsorption allowed the proposal of the reaction pathways and estimation of the role of all the catalyst components. It has been indicated that the introduction of calcium dopant to gold catalysts significantly increased the activity in methanol oxidation because of the synergistic interaction between both gold calcium components. The presence of niobium directed the selectivity of the reaction. The active species, their concentration, and oxidation states of all modifiers did not change during the reaction of methanol oxidation. The role of chemisorption of the reaction intermediates has been considered in detail.