Cinnamyl alcohol oxidation using supported bimetallic Au-Pd nanoparticles: An investigation of autoxidation and catalysis

In this study, we examine autoxidation and its role on the catalytic aerobic oxidation of cinnamyl alcohol using supported AuPd nanoparticles. We further report the crucial role of reaction conditions in the reaction pathway. Close attention is paid to the mechanism of the formation of benzaldehyde, a by-product formed in large quantities from the process of autoxidation. The activity of the catalysts depends on the preparation method with different sizes of nanoparticles obtained by the two methods of preparation. The catalysts can inhibit the autoxidation process or the two processes, namely catalytic oxidation and autoxidation, can coexist. In the case of oxidation of cinnamyl alcohol, 0.5%(wt) Au–0.5%(wt) Pd/TiO2 catalysts prepared by various methods allow different product distributions to be obtained. The catalyst prepared by the sol-immobilisation method seems to prevent autoxidation, leaving the catalytic process dominant. Catalysts prepared by the impregnation method seem to enable both the catalytic process and autoxidation to occur at the same time. We show that using the optimum catalyst for this reaction, the autoxidation process can be mitigated

The conversion of levulinic acid into γ-valerolactone using Cu-ZrO <inf>2</inf> catalysts

A series of Cu–ZrO2 catalysts prepared by a co-precipitation method were studied for the hydrogenation of levulinic acid to give γ-valerolactone (GVL). The effects of a range of catalyst preparation parameters, namely molar Cu/Zr ratio, calcination temperature and the ageing time of the precipitates, were systematically investigated. The molar Cu/Zr ratio was found to have a strong influence on the BET surface area of the material leading to a high activity for catalysts prepared with a Cu/Zr molar ratio of unity. Using this molar ratio the calcination temperature was varied from 300 °C to 800 °C, the material calcined at 400 °C showed the highest activity. Increasing the ageing time used in the catalyst preparation identified 6 h as the optimum to achieve the highest activity for LA conversion. Based on characterisation of all materials we conclude that the active Cu species is present in only low concentration suggesting that it should be possible to produce a catalyst of high activity with much lower Cu content

xNi–yCu–ZrO<inf>2</inf> catalysts for the hydrogenation of levulinic acid to gamma valorlactone

We have investigated xNi–yCu–ZrO2 catalysts for the selective synthesis of γ-valerolactone from levulinic acid (LA). A series of xNi–yCu–ZrO2 catalysts with a consistent metal loading of 50% but varying Ni and Cu composition were prepared by an oxalate gel precipitation method and tested for LA hydrogenation. Ni-rich catalysts showed higher catalytic activity compared with Cu-rich formulations with a 45Ni–5Cu–ZrO2 composition yielding 76% γ-valerolactone after a reaction time of 30 min at 200 °C. Characterisation of the materials by XRD, surface area measurements and TPR allow us to attribute the differences in performance seen for different compositions to particle size and nanoparticle dispersion effects. DFT calculations also showed that a shift of d-band centre to higher energies with the mole fraction of Ni in Cu–Ni alloys would be expected to lead to improved hydrogen dissociation in Ni-rich catalysts and so aid hydrogenation activit

Conversion of furfuryl alcohol into 2-methylfuran at room temperature using Pd/TiO<inf>2</inf> catalyst

The selective hydrogenation of furfuryl alcohol into 2-methylfuran was investigated at room temperature using palladium supported catalysts. We have shown that Pd–TiO2 catalysts can be very effective for the synthesis of 2-methylfuran at room temperature and low pressure of hydrogen (1–3 bar). The effect of various reaction conditions (pressure, catalyst amount, and solvent) was studied

The Effects of Dopants on the Cu-ZrO <inf>2</inf> Catalyzed Hydrogenation of Levulinic Acid

Catalytic hydrogenation of levulinic acid to form γ-valerolactone was studied over Cu–ZrO2 catalysts doped with metal oxides from the first-row transition metals. The Cu–ZrO2 material was prepared by oxalate gel coprecipitation, and dopants were added by an incipient wetness approach. The addition of 1% Mn into Cu–ZrO2 significantly increases the yield of γ-valerolactone, and the catalytic activity of Mn/Cu–ZrO2 was found to be 1.6 times higher than that of the undoped Cu–ZrO2 catalyst. Catalyst characterization suggests that the Mn dopant improves the dispersion of Cu on the surface of ZrO2. Kinetic studies show that the reaction order with respect to the substrate concentration is approximately zero. However, the order of reaction with respect to the partial pressure of H2 is different for the Mn/Cu–ZrO2 and Cu–ZrO2 catalysts. Comparison of reaction products from reactions carried out in H2O and D2O solvents using 1H NMR and 13C NMR show that there is a pre-equilibrium keto–enol isomerization step under our reaction conditions. DFT calculations show that the enol isomers have a higher affinity for the Cu surface, which may improve the availability of the substrate in the hydrogenation step of the reaction