resumo
Polyoxometalates (POMs) of series [PMo12-nVnO40](3+n)- (n = 1,2) supported on cellulose-silica hybrids (ca. 2 % w/w) exhibited high catalytic activity in gaseous aerobic oxidation of formaldehyde (CH2O) at room temperature. The oxidation of CH2O carried out in a packed-bed tubular reactor at a linear velocity of ca. 0.35 m/s and about 0.5 s residence time resulted in carbon dioxide and water as the main reaction products. The relative rate of CH2O oxidation at 294 K ranged from 1.5 x 10-2 to 2.7 x 10-2 molCH2O/(molcat s), i.e. ca. 0.35-0.49 g/(kgcat min) of catalytic material. The catalyst activity is determined by the reversible redox conversion V(V)<-> V (IV) in POMs under aerobic conditions. The efficiency of POMs in the oxidation of CH2O and their re-oxidation with dioxygen is affected by its electrostatic interaction with a supporting material, as revealed by phosphorus solidstate nuclear magnetic resonance (31P MAS NMR) and electron paramagnetic resonance (EPR) spectra. A mixed electron transfer/autoxidation mechanism has been proposed for the oxidation of CH2O in the aerobic catalytic system. Oxidation of CH2O by oxygen in the presence of POMs may include oxygen transfer via transient peroxomolybdate species, as elucidated by Raman spectroscopy. The catalysts maintained their activity after more than 300 turnovers thus allowing the continuous oxidation of CH2O in polluted air, at concentrations below 50 ppm.
palavras-chave
ULTRAVIOLET PHOTOCATALYTIC OXIDATION; AEROBIC OXIDATION; MOLECULAR-OXYGEN; POLYOXOMETALATE; AIR; H5PV2MO10O40; PERFORMANCE; REACTIVITY; COMPLEXES; POLLUTANT
categoria
Engineering
autores
Granja, ARS; Gamelas, JAF; Gamelas, JAF; Portugal, I; Evtuguin, D
nossos autores
Dmitry Evtyugin
Professor Associado com Agregação
Inês Portugal
Professor Auxiliar
José António Ferreira Gamelas
Bolseiro de pós-DoutoramentoProjectos
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
agradecimentos
This work was supported by CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020) , UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020) financed by national funds through the FCT/MEC (PIDDAC) .