Comparison between catalytic and catalytic photo-assisted propene hydration by using supported heteropolyacid

Abstract

Hybrid materials have been prepared by impregnation of the heteropolyacid H 3PW 12O 40 on commercial TiO 2. The polyoxometalates (POM) amount deposited was 15, 30, 50 and 70% with respect to the weight of the TiO 2 support. Moreover two samples containing a POM amount of 15, and 50% with respect to the weight of SiO 2 were also prepared for the sake of comparison. All prepared samples were efficient catalysts for the hydration of propene to 2-propanol in gas-solid regime at atmospheric pressure and at temperatures ranging between 50 and 85 °C. The study carried out on the hybrid TiO 2 based materials evidenced that, as far as the catalytic activity is concerned, exists an optimum in the amount of POM. Notably the contemporary presence of heat and UV light improved the activity of the POM/TiO 2 and POM/SiO 2 materials, although POM/TiO 2 showed better catalytic and catalytic photo-assisted activity than POM/SiO 2. POM species played a key role in both the catalytic and photo-assisted catalytic reactions, due to its surface acidity and ability to form strong oxidant species under UV irradiation. The presence of TiO 2 under UV irradiation improved the heteropolyacid performance supplying conduction band electrons to the POM

Keggin heteropolyacid H3PW12O40 supported on different oxides for catalytic and catalytic photo-assisted propene hydration

“…The set-up of the system was reported elsewhere. 35 A porous glass septum in the inlet of the flow allowed to distribute homogeneously the gaseous mixture. The reactivity runs were carried out with 0.5 g of solid powder by simply dispersing it as a thin layer inside the photoreactor (the fixed bed height was ca.…”

“…[27][28][29] In a previous paper the catalytic and catalytic photo-assisted activity of the H 3 PW 12 O 40 POM supported on TiO 2 Evonik P25 and SiO 2 was studied and a beneficial role of the photocatalytically active support on the reaction rate was reported. 35 The contemporary presence of heat and UV light improved the activity of the POM supported materials for the propene hydration reaction and the catalytic photo-assisted reaction occurred at a higher rate than the catalytic one when the solid support was an irradiated semiconductor. In that case, the more significant increase of reactivity was justified by considering the ability of TiO 2 to transfer electrons from the conduction band to the activated POM* species.…”

“…As far as the catalytic photo-assisted reactions are concerned, in addition to the previous mechanism, a further key role is played by POM being photosensitized to POM* upon exposure to near UV light (see introduction). POM* has a strong oxidation power and can receive an electron from propene being reduced to a blue species (POM À ) 35 (notably the supported POM sample became of blue color in our system under irradiation). Propene carbocation formed coordinates a water molecule from the dioxonium species, hence transferring the positive charge to the oxygen atom.…”

Heteropolyacid‐Based Materials as Heterogeneous Photocatalysts

“…Heterogenized HPA enhances the activity by acting as an electron scavenger, which results in a delay in the recombination of h + and e -pairs, [35] and by catalyzing the photodegradation of the substrate by means of HPA -, which can react with molecular oxygen or another electrophilic species [36] (see Figure 4). The Keggin-type HPA supported on TiO 2 has been the most studied photocatalyst.…”

“…[36] and it is performed by an electron acceptor such as O 2 dissolved in the suspension or in the absence of O 2 by other electrophilic species. [37] In this microreview the reported literature on the use of HPA-based materials as heterogeneous photocatalysts for environmental purposes is presented, in particular for complete or partial oxidation or reduction of organic molecules.…”