Sol Immobilization Research Articles

Gold catalysts for the direct oxidation of aminoalcohols to aminoacids

Gold catalysts on different supports, prepared by sol immobilization and deposition–precipitation, were tested in aminoalcohol oxidation for the direct preparation of aminoacids. Nitrogen substitution appeared to be crucial for avoiding parallel reaction pathway, but also the reaction conditions play an important role. Basic conditions and moderate temperature (40 °C) represent a good compromise for enhancing selectivity to aminoacids. TiO 2 represents the most versatile support.

Au–Pd supported nanocrystals prepared by a sol immobilisation technique as catalysts for selective chemical synthesis

Catalysis by gold and gold-palladium nanoparticles has attracted significant research attention in recent years. These nanocrystalline materials have been found to be highly effective for selective and total oxidation, but in most cases the catalysts are prepared using precipitation or impregnation. We report the preparation of Au-Pd nanocrystalline catalysts supported on carbon prepared via a sol-immobilisation technique and these have been compared with Au-Pd catalysts prepared via impregnation. The catalysts have been evaluated for two selective chemical syntheses, namely, oxidation of benzyl alcohol and the direct synthesis of hydrogen peroxide. The catalysts have been structurally characterised using a combination of scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts prepared using the sol immobilisation technique show higher activity when compared with catalysts prepared by impregnation as they are more active for both hydrogen peroxide synthesis and hydrogenation, and also for benzyl alcohol oxidation. The method facilitates the use of much lower metal concentrations which is a key feature in catalyst design, particularly for the synthesis of hydrogen peroxide.

Catalytic Oxidation of Polyethylene Glycol Dodecyl Ether to Corresponding Carboxylic Acid by Gold, Palladium (Mono and Bimetallic) Nanoparticles Supported on Carbon

Mono and bimetallic catalysts based on Au and Pd nanoparticles were synthesized by sol immobilization method. The catalytic oxidation of polyethylene glycol dodecyl ether was performed using as-synthesized supported catalyst. The use of water as solvent and dioxygen as oxidant makes the reaction interesting from both an economic and environmental point of view. For 100 min, the conversion of polyethylene glycol dodecyl ether using Au–Pd/C bimetallic catalyst was 38%, showing an increase of 9% for Au/C and 15% for Pd/C respectively indicating that a synergetic effect exists between Au and Pd. For the Au–Pd/C catalyst, adding Au after the prior addition and reduction of Pd metal can form the most active catalyst.

Effect of Au in Cs 2.5H 1.5PVMo 11O 40 and Cs 2.5H 1.5PVMo 11O 40/Au/TiO 2 catalysts in the gas phase oxidation of propylene

The catalytic study of the gas phase oxidation of propylene has been carried out using heteropolyacids modified with gold. In addition, TiO 2 was used as the main support for heteropolyacids and gold. Propylene oxidation was performed under different reaction conditions and in all the cases water was introduced owing to the beneficial effect in the formation of oxygenated products. It was found that deposition methods of Au onto heteropolyacid and heat pre-treatment procedure significantly affected the activity and the distribution of the products: sol immobilization promoted the total oxidation, whereas impregnation method the selective oxidation mainly to acrolein and acetic acid, depending on other reaction conditions. Depositing Cs 2.5H 1.5PVMo 11O 40 salt onto a preformed 1.5%Au/TiO 2 a significant increase towards the formation of oxygenated products was observed at the expense of total combustion. In particular, acrolein was produced in a synergistic manner. FT-IR, XRD, XPS and TPR techniques were used for catalyst characterization.

Solvent free liquid phase oxidation of benzyl alcohol using Au supported catalysts prepared using a sol immobilization technique

Solvent free oxidation of benzyl alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for benzyl alcohol oxidation.

Gold on titania: Effect of preparation method in the liquid phase oxidation

The effect of preparation method (deposition-precipitation versus sol immobilisation method) and reduction method (calcination versus chemical reduction) on Au/TiO 2 catalysts for the liquid phase oxidation of glycerol has been studied. It was revealed that a different trend existed in terms of activity and distribution of products. The catalytic activity is shown to be dependent not only on the choice of the reduction method but also on the use of protective agent (PVA, THPC) for the stabilization of the gold colloids. In fact, the highest activity was found when a low temperature chemical reduction was employed on a Au/TiO 2 sample synthesised by the deposition-precipitation method. The use of a higher pre-treatment temperature or of a protective agent resulted in a lower activity but could be used to direct selectivity in oxidation reactions. The structural data (HRTEM and XPS) along with the catalytic results indicate that the combination of metallic Au 0 species with small particle size (2–5 nm) are responsible for the high activity observed in the liquid phase oxidation of glycerol.

Au, Pd (mono and bimetallic) catalysts supported on graphite using the immobilisation method: Synthesis and catalytic testing for liquid phase oxidation of glycerol

The selective oxidation of glycerol was performed using mono and bimetallic catalysts based on Au and Pd and supported on graphite. Moreover, the preparation of bimetallic systems (Au–Pd) was investigated by using different procedures based on sol immobilisation method. The results showed that the use of a bimetallic system significantly improved the activity with respect to the monometallic system; whereas, the selectivity to glyceric acid showed to be dependent upon the reaction temperature and the preparation method used.