Solvent-free selective oxidation of benzyl alcohol by molecular oxygen over uranium oxide supported nano-gold catalyst for the production of chlorine-free benzaldehyde

A detailed investigation on the production of chlorine-free benzaldehyde in the solvent-free oxidation of benzyl alcohol by O2 over nano-gold supported on U3O8 has been carried out. Influence of different catalyst parameters (different methods of gold deposition on U3O8, gold loading and particle size, and catalyst calcination temperature) and reaction conditions (reaction period and temperature) on the process performance has been studied. The catalyst containing gold at higher concentration and with smaller gold particles showed the better process performance (higher benzyl alcohol conversion and benzaldehyde yield or selectivity). The benzyl alcohol conversion is largely increased but the selectivity for benzaldehyde is slightly decreased (while that of benzyl benzoate is increased) with increasing the reaction period or temperature. In the presence of solvent (viz. tolune, p-xylene, DMF or DMSO), the process performance was found to be inferior to that observed in the absence of any solvent. Substituted benzyl alcohols also can be oxidized by O2 to corresponding aldehydes with high yield and/or selectivity, using the catalyst in the absence of any solvent

Epoxidation of styrene by TBHP to styrene oxide using barium oxide as a highly active/selective and reusable solid catalyst

Styrene can be oxidised by TBHP to styrene oxide with high selectivity/yield using barium oxide (with or without gallium oxide support) as a simple, inexpensive and reusable solid catalyst; compared to the other alkaline and rare earth metal oxides, barium oxide showed a much better performance in the styrene epoxidation

A green process for chlorine-free benzaldehyde from the solvent-free oxidation of benzyl alcohol with molecular oxygen over a supported nano-size gold catalyst

Benzyl alcohol is oxidized selectively to benzaldehyde with high yield, with a little formation of benzylbenzoate, by molecular oxygen over a reusable nano-size gold catalyst supported on U3O8, MgO, Al2O3 or ZrO2 in the absence of any solvent

Direct oxidation of H<SUB>2</SUB> to H<SUB>2</SUB>O<SUB>2</SUB> over PdO/Al<SUB>2</SUB>O<SUB>3</SUB> catalysts in aqueous acidic medium: Influence on H<SUB>2</SUB>O<SUB>2</SUB> formation of Pd loading, calcination temperature and reduction of catalyst and presence of halide anions

Effects of the Pd loading (0.2-10 wt%), calcination temperature (400-900 ° C) and reduction of PdO/Al<SUB>2</SUB>O<SUB>3</SUB> on its performance in the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation (with H<SUB>2</SUB>/O<SUB>2</SUB> = 1:1) in an aqueous 0.1 M H<SUB>3</SUB>PO<SUB>4</SUB> medium, in the absence and presence of different halide anions, under ambient conditions have been investigated. The effect of calcination temperature on the H<SUB>2</SUB>O<SUB>2</SUB> formation varied depending upon the Pd loading. The influence of the different halide anions was found to depend strongly on the nature of halide anion (F<SUP>-</SUP>, Cl<SUP>-</SUP>, Br<SUP>-</SUP> or I<SUP>-</SUP>) and the oxidation state of Pd and its loading in the catalyst

Direct H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation over highly active/selective Br-F-Pd/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst in aqueous acidic medium: Influence of O<SUB>2</SUB>/H<SUB>2</SUB> ratio and other reaction conditions on the H<SUB>2</SUB>O<SUB>2</SUB> formation

The influence of the O<SUB>2</SUB>/H<SUB>2</SUB> mole ratio in the gaseous feed and also those of other reaction conditions [viz. concentration of H<SUB>3</SUB>PO<SUB>4</SUB> (0-5 mol/dm<SUP>3</SUP>), temperature (5-50 ° C), gas (H<SUB>2</SUB> and O<SUB>2</SUB>) space velocity (5.8-23.4 h-1) and reaction time (0.1-8 h)] on the H<SUB>2</SUB>O<SUB>2</SUB> formation in the H2-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation over the Br(1 wt%)-F(1 wt%)-Pd(5 wt%)/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst in an aqueous acidic (H3PO4) medium have been thoroughly investigated. The effects of the O<SUB>2</SUB>/H<SUB>2</SUB> ratio, reaction temperature and acid concentration on the destruction of H<SUB>2</SUB>O<SUB>2</SUB> by its decomposition and/or hydrogenation reactions over the catalyst in the acidic reaction medium have also been studied. The net H<SUB>2</SUB>O<SUB>2</SUB> formation (H<SUB>2</SUB>O<SUB>2</SUB> yield) over the catalyst passed through a maximum with increasing the acid concentration, the temperature or the O<SUB>2</SUB>/H<SUB>2</SUB> feed ratio. However, it decreased markedly with increasing the gas space velocity or the reaction period. The H<SUB>2</SUB>O<SUB>2</SUB> decomposition and hydrogenation activities of the catalyst increased appreciably with increasing the reaction temperature and decreased with increasing the acid concentration. The H<SUB>2</SUB>O<SUB>2</SUB> destruction during the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation increased with increasing the concentration of H<SUB>2</SUB> (relative to that of O<SUB>2</SUB>) due to the increased H<SUB>2</SUB>O<SUB>2</SUB> hydrogenation rate over the catalyst. The net H<SUB>2</SUB>O<SUB>2</SUB> formation in the H2-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation decreased sharply with increasing the initial amount of H2O2 present in the reaction mixture. The presence of H<SUB>2</SUB>O<SUB>2</SUB> and the higher H<SUB>2</SUB>/O<SUB>2</SUB> ratios have detrimental effects on the net formation of H<SUB>2</SUB>O<SUB>2</SUB>

Synergetic effect of two halogen promoters present in acidic reaction medium or catalyst on the H<SUB>2</SUB>O<SUB>2</SUB> formation (in H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation) and destruction over Pd/C (or Al<SUB>2</SUB>O<SUB>3</SUB>) catalyst

A strong synergetic effect of two different halide anions (F- and I-, Cl- and I-, Cl- and Br-, and F- and Br-) at optimum concentration in the catalyst or in an acidic reaction medium was observed in the H2-to-H2O2 oxidation over Pd/C, Pd/Al2O3, and halogenated Pd/Al2O3 catalysts. The synergetic effect promotes the net H2O2 formation by inhibiting the H2O2 decomposition and hydrogenation reactions. The effect is most pronounced for the combination of fluoride (or chloride) and iodide anions. The Br (1 wt%)-F (1 wt%)-Pd (5 wt%)/Al2O3 catalyst showed very high H2O2 yield (59%)/selectivity (60%) in the H2-to-H2O2 oxidation

Hydrogenation of hydrogen peroxide over palladium/carbon in aqueous acidic medium containing different halide anions under static/flowing hydrogen

Kinetics of the hydrogenation of hydrogen peroxide (at 278 and/or 300 K) over Pd(5 wt%)/carbon in aqueous medium with or without containing acid or different halide anions (F-, Cl-, Br-, or I-) under static H2 (i.e. batchwise) or flowing H2 (i.e. semi-batchwise) at atmospheric pressure have been thoroughly studied. In the absence of protons or halide anions and also in the presence of F- anions, a very rapid decomposition of H2O2 (H2O2 &#8594; H2O + 0.5O2) predominates over the H2O2 hydrogenation (H2O2 + H2 &#8594; 2H2O). However, in the presence of both the protons and Cl- or Br- anions, the H2O2 conversion occurs mainly by the hydrogenation reaction. The hydrogenation is found to be a zero-order reaction with respect to the H2O2 concentration, and its activation energy and frequency factor are strongly influenced by the halide anions. The hydrogenation is found to be more and more inhibited with increasing halide (Cl- or Br-) anion concentration. The cations associated with the halide anions have, however, only a very little influence on the hydrogenation. Iodide anions act as a very strong catalyst poison for the hydrogenation. In the presence of acid, the hydrogenation is very strongly influenced by the different halides, but, in the presence of halide anions (5.4 mmol/dm3), it is very mildly influenced by the different mineral acids (except HI). In the absence of protons, the Cl- and Br- anions are ineffective for inhibiting the rapid H2O2 decomposition. A role played by protons and halide anions for drastically inhibiting the rapid H2O2 decomposition is discussed

In situ generation of hydrogen peroxide from reaction of O<SUB>2</SUB> with hydroxylamine from hydroxylammonium salt in neutral aqueous or non-aqueous medium using reusable Pd/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst

In situ generation of H<SUB>2</SUB>O<SUB>2</SUB> with high yield can be accomplished by reacting O<SUB>2</SUB> with NH<SUB>2</SUB>OH from hydroxylammonium salt [NH<SUB>2</SUB>OH . HCl or (NH<SUB>2</SUB>OH)<SUB>2</SUB> . H<SUB>2</SUB>SO<SUB>4</SUB>] in a neutral aqueous medium using a reusable heterogeneous Pd (1.0 wt%)/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst, even at low temperature (10°C), with the formation of harmless by-products (viz. N<SUB>2</SUB> and water). The presence of KCl or KBr in the medium has beneficial effect. The H<SUB>2</SUB>O<SUB>2</SUB> generation is strongly influenced by the pH of medium, reaction period and temperature; best results are obtained at the optimum pH and reaction medium

Direct oxidation of H<SUB>2</SUB> to H<SUB>2</SUB>O<SUB>2</SUB> over different supported PdO Catalysts in aqueous acidic medium: Influence of the calcination temperature, reduction and support of the catalyst on its net H<SUB>2</SUB>O<SUB>2</SUB> formation activity

Effects of the catalyst reduction (by hydrazine), calcination temperature (400-800 ° C) and support (viz. Al<SUB>2</SUB>O<SUB>3</SUB> , SiO<SUB>2</SUB>, CeO<SUB>2</SUB>, ZrO<SUB>2</SUB>, Hβ or HM) on the performance of supported PdO (2.5 wt%) catalyst in the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2 </SUB> oxidation (with H<SUB>2</SUB>:O<SUB>2</SUB> = 1:1) in an aqueous acidic (0.1 M H<SUB>3</SUB>PO<SUB>4</SUB>) medium under ambient conditions have been investigated. All the supported PdO catalysts showed lower H<SUB>2</SUB> conversion activity, but higher H<SUB>2</SUB>O<SUB>2</SUB> selectivity, as compared to their reduced counter parts. The catalyst performance for the net H<SUB>2</SUB>O<SUB>2 </SUB>formation is strongly influenced by both the support and calcination temperature of the supported PdO catalysts. The catalysts calcined at 400 ° C showed better performance. Among the catalysts, PdO/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst (calcined at 400 ° C) showed the best performance (17.0% H<SUB>2</SUB>O<SUB>2 </SUB> yield) in the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2 </SUB> oxidation. The influence of the calcination temperature of PdO/Al<SUB>2</SUB>O<SUB>3</SUB>catalyst on its H<SUB>2</SUB>O<SUB>2 </SUB> decomposition and hydrogenation activities has also been investigated. Both the H<SUB>2</SUB>O<SUB>2 </SUB> decomposition and hydrogenation activities increased with increasing the calcination temperature

Formation from direct oxidation of H<SUB>2</SUB> and destruction by decomposition/hydrogenation of H<SUB>2</SUB>O<SUB>2</SUB> over Pd/C catalyst in aqueous medium containing different acids and halide anions

Direct oxidation of H<SUB>2</SUB> by O<SUB><SUB>2</SUB></SUB> to H<SUB>2</SUB>O<SUB>2</SUB> and decomposition/hydrogenation of H<SUB>2</SUB>O<SUB>2</SUB> (at 27176;C and atmospheric pressure) over Pd/C catalyst in an aqueous acidic reaction medium have been thoroughly investigated using different mineral acids (viz. 0.1N H<SUB>2</SUB>SO<SUB>4</SUB>, H<SUB>3</SUB>PO<SUB>4</SUB>, H<SUB>3</SUB>BO<SUB>3</SUB>, HNO<SUB>3</SUB>, HCl, HBr or HI) and/or halide anions (viz. F<SUP>-</SUP>, Cl<SUP>-</SUP>, Br<SUP>-</SUP>or I<SUP>-</SUP>), covering their wide concentration range (0-24 mmol/dm<SUP>3</SUP>), in the reaction medium. In the absence of any externally added halide, appreciable H<SUB>2</SUB>O<SUB>2</SUB> formation in the H<SUB>2</SUB> oxidation occurred only when the medium contained HCl. However, the rates of H<SUB>2</SUB>O<SUB>2</SUB> decomposition and hydrogenation are greatly reduced because of the presence of any acid; the influence on the H<SUB>2</SUB>O<SUB>2</SUB> decomposition was, however, much larger for the halo acids. In the presence of acid (0.1N H<SUB>3</SUB>PO<SUB>4</SUB> or H<SUB>2</SUB>SO<SUB>4</SUB>), the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> formation reaction is greatly enhanced by the externally added halide anions up to their optimum concentrations. However, above the optimum halide anion concentration, it is inhibited more than the H<SUB>2</SUB>-to-water formation (parallel) reaction, causing a decrease in both the H<SUB>2</SUB>O<SUB>2</SUB> yield and selectivity. Whereas, the H<SUB>2</SUB> conversion and H<SUB>2</SUB>O<SUB>2</SUB> destruction activities of the catalyst are decreased continuously with increasing the halide anion (except F<SUP>-</SUP>) concentration. Among the halides, chloride is the best halide promoter for Pd/C catalyst in the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation. At the optimum Cl<SUP>-</SUP> concentration (5.4 mmol/dm<SUP>3</SUP>), both the H<SUB>2</SUB> conversion and H<SUB>2</SUB>O<SUB>2</SUB> yield are passed through a maximum and the H<SUB>2</SUB>O<SUB>2</SUB> decomposition is greatly inhibited with increasing the phosphoric acid concentration. In the absence of either the chloride anions or the acid (or both) in the reaction medium, only a little or no H<SUB>2</SUB>O<SUB>2</SUB> is formed in the H<SUB>2</SUB> oxidation and also the rate of H<SUB>2</SUB>O<SUB>2</SUB> destruction is very fast, particularly in the presence of H<SUB>2</SUB>; the rapid destruction of H<SUB>2</SUB>O<SUB>2</SUB> is mainly due to its decomposition rather than its hydrogenation. The best H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation results are obtained at the optimum concentrations of both the acid and halide anions. In the presence of acid and chloride (or bromide) promoter, the H<SUB>2</SUB>O<SUB>2</SUB> hydrogenation dominates the H<SUB>2</SUB>O<SUB>2</SUB> destruction and hence the net H<SUB>2</SUB>O<SUB>2</SUB> formation is mainly controlled by the H<SUB>2</SUB>O<SUB>2</SUB> hydrogenation