Partial oxidation of toluene to benzaldehyde catalyzed by heteropoly compounds immobilized on activated carbon

A series of studies of hydrocarbon oxidation by the O2 + H2 mixture in the presence of catalytic systems based on Pt or Pd and a heteropoly compound (HPC) is reviewed. The catalytic systems were prepared from Pd(II) complexes with the heteropoly tungstate anions PW11O 29 7− and PW9O 34 9− , the complex salt [Pt(NH3)4][H2Mo12O40]2 · 7H2O, mixtures of H2PtCl4 or H2PtCl6 with H3 + n PMo12 − n V n O40 (n = 0–3) heteropoly acids, or supported platinum dispersed in HPC solutions. The interaction of metal ions and particles with HPCs in the initial state and after thermal and redox treatments was investigated by NMR, IR spectroscopy, XPS, EXAFS, HREM, and TPR. The catalytic systems were tested in the liquid-phase oxidation of alkanes, cyclohexane, cycloalkenes, benzene, toluene, and phenol with the O2 + H2 mixture at low temperatures. Effective supported catalysts based on platinum nanoparticles associated with the redox-active HPCs H3PMo12O40 and H4PMo11VO40 were prepared for gas-phase benzene oxidation into phenol. The oxidation mechanism includes the interaction between dioxygen and platinum (or palladium) and the participation of the HPC in the formation of active oxygen species of radical nature.

Structure-Activity Relationships in the Oxidation of Alkylaromatics Over Metal Oxides

Perovskite type oxide are known to be catalysts for a number of reactions such as total and partial oxidation, hydrocracking, hydrogeneous, hydrogenolysis and reduction etc. Efforts has largely been directed towards synthesis of unsupported and supported perovskites oxides of moderates or high specific area, their bulk and surface properties and their role in heterogenous catalysis. Oxidation of aromatic and aliphatic hydrocarbon over LaMO3 (M=Al, Ni, Mn, Co, Fe, Cr etc.) perovskites have been studied. Vapour phase catalytic oxidation of toluene over perovskites Viz., LaCoO3, LaCoO3/ SiO2 and LaCoO3/Al2O3 has been studied. The characterization of the catalyst was carried out using technique Viz. I.R., Surface area, Packing density. Surface acidity, Surface basicity. The surface area measurements in the temperature range 350ºC to 600ºC. The maximum surface area & maximum activity was observed at 450ºC. The heterogeneous catalytic vapour phase oxidation of toluene give benzaldehyde, benzoic acid, maleic acid and CO2 as products over LaCoO3 and LaCoO3 supported on Al2O3 and SiO2 as catalyst. The LaCoO3 supported on Al2O3 has been found to be the most active and selective catalyst giving 84.0% selectivity for benzaldehyde at 450⁰C with surface area 78.9m2/g. The overall Kinetic analysis indicate that the oxidation of Toluene to benzaldehyde is first order. The order of catalytic reactivity is LaCoO3/Al2O3 > LaCoO3/ SiO2 > LaCoO3.

The gas-phase partial oxidation of benzene and toluene to phenol and to cresols over Fe-containing ZSM-5 zeolites prepared by various methods was studied using N2O as oxidant. Over FeZSM-5 synthesized by either isomorphous substitution or ion exchange the phenol selectivity reached nearly 100% at 573 K, however, only 25-30% cresol (mainly p-cresol) selectivity was observed in the oxidation of toluene because of the formation of benzaldehyde and benzoic acid in the fast oxidation of the methyl group.

A fuel cell system was used for the synthesis of benzaldehyde from toluene in the gas phase. The cell system [anode: Pd‐black with added : Pt‐black with added graphite] operated at ca. 373 K under short‐circuit conditions and produced the partial oxidation products benzaldehyde and benzoic acid . The addition of chlorides such as , , , etc., to the anode remarkably improved the selectivity of the sum of and . In the presence of chlorides, was not produced at all. Among the chlorides tested, is the best additive for the synthesis of . Kinetic results on the reaction with the anode have shown that decreasing temperatures and increasing pressures of the reactants (toluene and ) favor the oxidation to . The oxidation of toluene under an externally applied potential showed a product distribution similar to that observed under short‐circuit conditions. The turnover number greater than unity (2.4) indicates catalytic cycling of the Pd in the anode. The current efficiency was improved by cyclic short‐ and open‐circuit operation of the cell. A reaction mechanism assuming a complex as the reaction intermediate explains the kinetic results and the favorable effect of chloride. The intermediate complex may be generated through the electrochemical oxidation of Pd and toluene. The subsequent competitive formations of and from this complex proceed nonelectrochemically.

Liquid phase oxidation of alkylaromatic hydrocarbons over titanium silicalites

DRIFT study of the oxidation and the ammoxidation of toluene over a TiO 2(B)-supported vanadia catalyst

Non‐aqueous phase liquids (NAPLs), such as toluene, often contaminate the subsurface. In this study, we focus on the transformation of toluene NAPL trapped in a single glass replica of a rock fracture via in situ chemical oxidation (ISCO) with ferrous activated persulfate. The trapped toluene consisted of a main trapped blob surrounded by smaller blobs. Over 53 days, successive persulfate injections into the fracture were interspersed with periods of water flushing. During persulfate injections, effluent toluene concentrations were below 0.04 mM. The rebound toluene concentrations during intervening water flushing periods decreased from 0.9 to 0.3 mM over the study. The smaller toluene blobs were removed by dissolution and partial oxidation. The main toluene blob was reduced in area by 35.5% and in volume by 37.3% due to dissolution and partial oxidation. The main blob changed in shape with reduction in size and there was also formation of an oxidation by‐product zone around the blob. The reduction in toluene effluent concentrations with time over successive persulfate injections and periods of water flushing was attributed to reductions in the NAPL‐water interfacial area of the blob and the formation of the by‐product zone surrounding the blob, which resulted in limited toluene dissolution. Analysis of by‐products of toluene oxidation by ferrous activated persulfate suggests that oligomers were part of the by‐product zone formed in the fracture. Gas bubbles were also observed in the fracture and may have formed from toluene oxidation and persulfate decomposition.

Effect of potassium doping on the structural and catalytic properties of V/Ti-oxide in selective toluene oxidation

A series of Cs2Te0.2H0.6 + x PMo12 − x V x O n (x = 0–3) heteropoly compounds has been prepared and tested in the partial oxidation of isobutane. Catalytic tests show that at 350°C very high selectivity to methacrylic acid (60.1%) can be achieved at isobutane conversion of 12.2% over a Cs2.0Te0.2H1.6PMo11VO n catalyst with only one molybdenum atom per unit cell substituted by vanadium. The presence of Te4+ in the heteropoly compounds appears to interfere with the dehydrqgenation step and favor the formation of methacrolein and methacrylic acid.

Fabricate and characterization of Ag/BaAl2O4 and its photocatalytic performance towards oxidation of gaseous toluene studied by FTIR spectroscopy

Activity and selectivity in the oxidation of toluene on unsupported and supported V2O5 catalysts (V2O5/TiO2 and V2O5/Al2O3) have been investigated in terms of the catalyst structure under the following conditions: total pressure, 1 atm (1 atm ≈ 101.3 kPa); partial pressure of toluene, 0.041 atm; partial pressure of O2, 0–0.861 atm; temperature, 588–644 K. The results under various contact times indicated that partial oxidation to benzaldehyde, benzoic acid and maleic anhydride proceeds concurrently with the total oxidation to carbon oxides on the vanadium oxide catalyst. It was also found that the surface VO species plays the active oxygen species and that the activity is mainly determined by the number of surface VO species for both unsupported and supported catalysts. Although the selectivity to partial oxidation products (Sp) was independent of the oxidation state of the vanadium oxide, it was greatly affected by the roughness of the catalyst surface and rough V2O5 was favourable for the selective oxidation. This provides a new type of structure–selectivity correlation for the vanadium oxide and has never been observed for the oxidation of benzene, but-1-ene, buta-1,3-diene or furan. In agreement with the correlation, the mode of change in the selectivity with the structure of supported catalysts was much different from that for previous reactions and was explained in terms of the change in surface roughness. A mechanism is also proposed to explain the new structure–activity/selectivity correlation for the toluene oxidation.

The effects of reaction conditions and concentration of the heteropoly acid H4PMo11VO40 supported onto ShAS-2 bead aluminosilicate on the conversion of toluene into benzoic acid in the partial oxidation of toluene by atmospheric oxygen were studied. The results demonstrated that the conversion of toluene was an extremal function of temperature, space velocity (v), and toluene concentration (C0) in the initial air mixture. An increase in the heteropoly acid concentration from 2 to 30% increased the conversion of toluene into benzoic acid in the partial oxidation of toluene from 1.5 to 12.6% at optimum process parameters: T = 300°C, v = 2000 h-1, and C0 = 13.72 g/m3.

The oxidation of toluene on various molybdenum-containing catalysts

Crystalline structures of USb 3O 10 and USbO 5 in acrylonitrile catalysts