CATALYSIS BY 12-MOLYBDOPHOSPHATES .1. CATALYTIC REACTIVITY OF 12-MOLYBDOPHOSPHORIC ACID-RELATED TO ITS THERMAL-BEHAVIOR INVESTIGATED THROUGH IR, RAMAN, POLAROGRAPHIC, AND X-RAY-DIFFRACTION STUDIES - A COMPARISON WITH 12-MOLYBDOSILICIC ACID

The thermal behavior of 12-molybdophosphoric acid (PMo12H) was investi gated using coupled techniques (IR and Raman spectroscopies, polarogra phy, X-ray diffraction, and catalytic reactivity in methanol oxidation ) and compared with results obtained with 12-molybdosilicic acid. The decomposition of PMo12H occurs in a wide temperature range, leading to mixtures of beta- and alpha-MoO3, A great analogy between the P and S i compounds is evidenced outside the decomposition range, The differen ces inside this range (wide for P, narrow for Si compound) are discuss ed in terms of kinetics of decomposition, textural evolution, and capa bility to rebuild the Keggin unit, (C) 1996 Academic Press, Inc.