One-pot Hydrothermal Synthesis of Mesoporous V-SBA-16 with a Function of the pH of the Initial Gel and its Improved Catalytic Performance for Benzene Hydroxylation

Increasing the Efficiency of Optimized V-SBA-15 Catalysts in the Selective Oxidation of Methane to Formaldehyde by Artificial Neural Network Modelling

The present study investigates the possibility of improving the selective oxidation of methane to formaldehyde over V-SBA-15 catalysts in two different ways. In a classical approach of catalyst optimization, the in situ synthesis of V-SBA-15 catalysts was optimized with regard to the applied pH value. Among the set of catalysts synthesized, a higher amount of incorporated vanadium, a higher content of polymeric VOx species as well as a less ordered structure of the support material were observed by increasing the pH values from 2.0 to 3.0. An optimum in performance during the selective oxidation of methane to formaldehyde with respect to activity and selectivity was found over V-SBA-15 prepared at a pH value of 2.5. With this knowledge, we have now evaluated the possibilities of reaction control using this catalyst. Specifically, artificial neural network modelling was applied after the collection of 232 training samples for obtaining insight into the influence of different reaction parameters (temperature; gas hourly space velocity (GHSV); and concentration of O2, N2 and H2O) onto methane conversion and selectivity towards formaldehyde. This optimization of reaction conditions resulted in an outstanding high space-time yield of 13.6 kgCH2O∙kgcat∙h−1.

Polyoxometalates acting as a hole-transfer mediator and crystallization accelerant in a perovskite photoanode for the photoelectrocatalytic oxidation of benzene into phenol

Organic metal halide perovskite (OMHP) material shows promising applications in the photoelectrocatalytic field, but its efficiencies are unsatisfactory due to the bulk and surface carrier recombination. In this work, we used dual polyoxometalates (C₄H₉N)₃PW₁₂O₄₀ and [Ag₁₀[{Co(H₂O)₃}₂{CoBi₂W₁₉O₆₆(OH)₄}] to modify the OMHP photoanode; the former acted to improve the quality of the perovskite film and the latter could facilitate hole transfer. Such dual modifications effectively reduce carrier recombination and thus obviously boost photoelectrocatalytic efficiency. Hence, we explored the photoelectrocatalytic oxidation of benzene into phenol in aqueous solution by using the modified OMHP photoanode. The yield of phenol in the reaction using the modified OMHP photoanode reached about 31.8%, which was obviously superior to that using the pure OMHP photoanode. Furthermore, we carried out radical scavenger studies to investigate the active species involved in the photoelectrocatalytic benzene oxidation reaction, and thus proposed the plausible mechanism of the photoelectrocatalytic oxidation of benzene into phenol over the OMHP photoanode. These results provide new insights into the development of high performance OMHP photoanodes for photoelectrocatalytic organic transformation.

The design, synthesis and catalytic performance of vanadium-incorporated mesoporous silica with 3D mesoporous structure for propene epoxidation

Novel promising vanadium catalysts based on mesoporous silica of 3D structure, namely KIT-6, SBA-12, and MCF, for the direct propene epoxidation with N₂O.

One-pot synthesis of vanadium-containing silica SBA-3 materials and their catalytic activity for propene oxidation

V-containing silica SBA-3 mesoporous catalysts were prepared by means of one-pot hydrothermal procedure with NH₄VO₃ or VOSO₄ as vanadium precursors under various acidic medium of the reaction mixture (pH < 1, 2.2 or 3.1). The combined spectral techniques (DR UV-vis, FTIR, EPR) as well H₂-TPR allowed to determine the nature of vanadium species in the studied samples. A successful incorporation of vanadium into the structure of silica SBA-3 was attained for the samples with low V content (<1 wt%), whereas the V-rich samples (i.e. >5 wt%) exhibited the presence of isolated vanadium and also of polynuclear surface species. The resulting V-bearing samples contain the Brønsted and Lewis acidic centres evidenced by FTIR spectra of adsorbed pyridine and by catalytic activity for 2-propanol decomposition and cumene cracking. Ammonia TPD allowed to estimate the number and strength of acid sites in regards to the vanadium content. Propene oxidation with N₂O revealed noticeable activity of the synthesised V-SBA-3 samples in epoxidation reaction. On the basis of TOF analysis indicating the activity of particular vanadium ions it seems that not all of the introduced V atoms take part in the formation of mild electrophilic oxygen species responsible for propene oxide formation.

Efficient SBA-3 vanadosilicate catalysts for propene oxidation obtained for the first time by the one-pot synthesis.

Textural and morphology changes of mesoporous SBA-15 silica due to introduction of guest phase

The research focuses on study of guest phase effect on the surface area and pore volume of SBA-15 with the emphasis on elucidation of reasons for these changes. The changes of surface area and pore volume are evident from evaluated N2 adsorption isotherms of VOx-SBA-15 even for samples with relative low content of supported guest phase, which is “atomically” spread on the surface in the form of anchored monomeric vanadyl species. These species cannot block the pore with diameter of 10 nm, nevertheless the presence of such phase causes decrease in adsorbed nitrogen during physisorption. Comparison of guest phase amount with differences in adsorbed amount of nitrogen led to conclusion that each vanadyl complex prevents adsorption of about one or two N2 molecules in the layer and influences two adsorption layers. Significant pore blocking occurs in the VOx-SBA-15 materials only in the case of presence bulk oxide-like nanospecies. Re-structuralization of silica mimicking phase separation phenomena relying on spinodal decomposition of a system was observed by SEM/TEM analysis and adsorption isotherms inspection for materials with high vanadium content.

VxOy@C catalyst prepared from biomass for hydroxylation of benzene to phenol with molecular oxygen

The selectivity of phenol for the hydroxylation of benzene was found to be related to the adsorption of phenol on the V_xO_y@C catalyst.