The role of protons in acid-base type reactions on heteropolyacid catalysts: gas-phase MTBE synthesis on H4SiW12O40

Basing on the kinetic and sorption experiments a mechanism of catalytic for mation of methyl-tert-butyl ether (MTBE) on H4SiW12O40 was proposed. A reac tion intermediate, carbenium ion C4H9+, is forming at the catalyst surface from isobutene supplied from gas phase and protons supplied by the solid. S ubsequently C4H9+ reacts with methanol absorbed by the solid heteropolyacid . The model satisfactorily explains the anomalous reaction order with respe ct to methanol which under the applied conditions is positive at the initia l stage of the catalytic process and becomes negative at its steady state.