Structural Evolution under Reaction Conditions of Supported (NH4)3HPMo11VO40 Catalysts for the Selective Oxidation of Isobutane

Abstract

When using heteropolycompounds in the selective oxidation of isobutane to methacrolein and methacrylic acid, both the keeping of the primary structure (Keggin units) and the presence of acidic sites are necessary to obtain the desired products. The structural evolution of supported (NH4)3HPMo11VO40 (APMV) catalysts under preliminary thermal oxidizing and reducing treatments was investigated. Various techniques, such as TGA/DTG (Thermo-Gravimetric Analysis/Derivative Thermo-Gravimetry), H2-TPR (Temperature Programed Reduction), in situ XRD (X-Ray Diffraction) and XPS (X-ray Photoelectron Spectroscopy), were applied. It was clearly evidenced that the thermal stability and the reducibility of the Keggin units are improved by supporting 40% APMV active phase on Cs3PMo12O40 (CPM). The partial degradation of APMV takes place depending on temperature and reaction conditions. The decomposition of ammonium cations (releasing NH3) leads to the formation of vacancies favoring cationic exchanges between vanadium coming from the active phase and cesium coming from the support. In addition, the vanadium expelled from the ) to activate isobutane. The increase in reducibility of the supported catalyst is assumed to improve the catalytic performance in comparison with those of unsupported APMV.

Controllable Fabrication of Amorphous Co—Ni Pyrophosphates for Tuning Electrochemical Performance in Supercapacitors

“…Figure d shows the P 2p spectrum with a symmetric peak at 134.1 eV, suggesting a +5 state for all P atoms in the product . The O 2p spectrum in Figure e can be fitted as two peaks at 531.4 and 532.9 eV, corresponding to lattice oxygen and surface chemisorbed oxygen in hydroxyl, repectively. , The deconvolution results of the N 1s spectrum at binding energies of 399.8 and 401.9 eV are also shown in Figure f, which can be assigned to N 3− for the NH 3 and NH 4 + groups, repectivly. , …”

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…New types of catalysts for efficient oxidation of carbon-hydrogen compounds have been reported in recent years: heteropolycompounds [107][108][109][110], supported complex catalysts [111,112], and porous materials [113][114][115][116][117][118][119][120][121][122].…”

Cs(NH4)xH3–xPMo11VO40 Catalyzed Selective Oxidation of Methacrolein to Methacrylic Acid: Effects of NH4+ on the Structure and Catalytic Activity

“…Methacrylic acid (MAA), as an important chemical intermediate for synthesis of methyl methacrylate (MMA), was normally synthesized by selective oxidation of methacrolein (MAL) over Keggin-type polyoxometalates catalysts. − Among those screened, the cesium salts of 11-phosphomolybdovanadyl acids behaved with a good catalytic efficiency in the selective oxidation of MAL to MAA. − In recent years, ammonium-modified polyoxometalates received increasing attention − because they exhibited enhanced catalytic performance in the production of MAA . For instances, Otero Areán and Marosi found two extra-framework molybdenum ions coexisted in Cs x (NH 4 ) y H z PMo 12 O 40 , offering the conversion of 50.7% from MAL to MAA .…”