Role of Vanadium and Phosphorus in Substituted Keggin‐Type Heteropolyoxo Molybdates Supported on Silica SBA‐15 in Selective Propene Oxidation

Abstract

Vanadium‐containing Keggin‐type heteropolyoxo molybdate ([PV2Mo10O40]5−) was supported on silica SBA‐15 (denoted as PV2Mo10‐SBA‐15). The structural evolution and catalytic activity of PV2Mo10‐SBA‐15 and a suitable reference V2Mo10Ox‐SBA‐15 were investigated under selective propene oxidation conditions by using in situ X‐ray absorption spectroscopy. 31P MAS NMR measurements of supported PV2Mo10‐SBA‐15 and reference H3PO4‐SBA‐15 were performed after the catalytic reaction. PV2Mo10‐SBA‐15 formed a mixture of mainly tetrahedral [MoOx] and [VOx] units during thermal treatment under propene oxidation conditions. Changes in the average local structure around V centers coincided with the changes in the average local structure around Mo centers and the onset of catalytic activity. In addition, mainly tetrahedral [MoOx] and [VOx] units seemed to be in close proximity and interacted under catalytic conditions. Conversely, in the reference material V2Mo10Ox‐SBA‐15 synthesized with individual V and Mo source precursors, Mo and V centers appeared to be more separated from each other. The structural environment of P in PV2Mo10‐SBA‐15 under catalytic conditions corresponded to a mixture of various species. P was connected to both the support material SBA‐15 via POSi bonds and [MoOx] or [VOx] units. Apparently, the proximity of V and Mo in Keggin precursors was a prerequisite for obtaining (Mo,V) oxide species on the support material.

Correlation between Copper Oxide Particle Size and Selectivity towards Propylene Oxide in Selective Oxidation of Propene

“…Hence, the increase in activity with decreased copper loading might be caused by an increasing dispersion of copper oxide particles. Accordingly, small, well‐dispersed copper oxide particles exhibited an increased surface to bulk ratio and, thus, a higher activity in comparison to larger particles or bulk material ,. After 6 h time‐on‐stream, propene reaction rates of all CuO/SBA‐15 samples decreased and were largely independent of copper loading.…”

“…Accordingly, small, well-dispersed copper oxide particles exhibited an increased surface to bulk ratio and, thus, a higher activity in comparison to larger particles or bulk material. [7,49] After 6 h time-on-stream, propene reaction rates of all CuO/SBA-15 samples decreased and were largely independent of copper loading. All five CuO/SBA-15 samples exhibited a similar decrease in UV-Vis absorption edge energies and, hence, increase in particle size during time on stream ( Figure 5).…”

Effects of Anion Substitution in (Mo,V)5O14 on Catalytic Performance in Selective Propene Oxidation to Acrolein

“…Several examples from the literature show that supported and highly dispersed transition metal oxides species are also active in selective propene oxidation . Hence, migration of anion vacancy in the bulk may not be mandatory for catalytic activity.…”

“…Several examples from the literature show that supported and highly dispersed transition metal oxides speciesa re also active in selective propene oxidation. [48,49] Hence, migration of anion vacancy in the bulk may not be mandatory for catalytic activity.H owever,t he reoxidation of supported catalysts is also associated with at ransfer of electrons to adsorbed oxygen species on MÀOÀMu nits. Isolated monomeric species on support material showed very lowc atalytic activity owing to the missingt ransfer of electrons.…”

Direct templating assembly route for the preparation of highly-dispersed vanadia species encapsulated in mesoporous MCM-41 channel

“…[8][9][10][11][12][13][14] A series of derived mesoporous composites have also shown potential applications in biomedical science, 15 optical sensing, 16 and catalysis. [17][18][19] Supported vanadium oxide catalysts contain the vanadium oxide phase deposited on mesoporous silica and have found extensive applications as oxidation catalysts in the chemical and petroleum industries. In particular, the supported vanadia phase, presented as surface vanadium oxide species, is responsible for the overall catalytic activity and selectivity.…”