Isoprene Synthesis from Formaldehyde and Isobutene over Keggin-type Heteropolyacids Supported on Silicaстатья
Статья опубликована в высокорейтинговом журнале
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Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 3 октября 2016 г.
Аннотация:Gas phase Prins condensation of isobutene with formaldehyde has been studied over different Keggin-type heteropolyacids supported on amorphous silica. The catalysts were characterized by elemental analysis, X-ray diffraction, low temperature nitrogen adsorption, TPD of ammonia, FTIR of adsorbed pyridine and NMR spectroscopy. The activity of supported heteropoly compounds was found to increase in the following order: H4SiMo12O40 < H3PMo12O40 < H4SiW12O40 [approximate] H3PW12O40. Lower activity of supported molybdenum heteropolyacids was attributed to their low thermal stability and partial decomposition during catalysts activation, which resulted in lower acidity. The variation of HPA content from 5 to 33 wt % was also shown to increase the catalyst’s activity. Basing on the relationship between the content of weak Bronsted sites, the amount and type of carbonaceous deposits and the catalytic activity it was concluded that the generation of "working" active sites over HPA catalysts involves the formation of unsaturated branched surface species over weak Bronsted sites. These active carbonaseous species are responsible for the selective isoprene synthesis. The best catalyst performance is observed over the catalyst with 20 wt% of H3PW12O40, which show isoprene yields of 48% with selectivity of 63%.