Pierre Gallezot

Glycerol hydrogenolysis on heterogeneous catalysts

Aqueous solutions of glycerol were hydrogenolysed at 180 °C under 80 bar H2-pressure in the presence of supported metal catalysts in an attempt to selectively produce 1,2- and 1,3-propanediol. Catalysts (Cu, Pd, Rh), supports (ZnO, C, Al2O3), solvents (H2O, sulfolane, dioxane) and additives (H2WO4) were tested to improve reaction rate and selectivity to the target molecules. The best selectivity (100%) to 1,2-propanediol was obtained by hydrogenolysis of water solution of glycerol in the presence of CuO/ZnO catalysts. To improve the selectivity to 1,3-propanediol the reaction was conducted with rhodium catalysts with tungstic acid added to the reaction medium. The best result in terms of conversion and selectivity to 1,3-propanediol (1,3-PDO/1,2-PDO = 2) was obtained by operating in sulfolane. The presence of iron dissolved in the reaction medium was also beneficial for the selectivity to 1,3-PDO. A mechanism was proposed to account for the effect of these different parameters.

Chemoselective catalytic oxidation of glycerol with air on platinum metals

Abstract The transesterification of triglycerides extracted from oilseeds to obtain biodiesel fuel yields up to 14% by weight of glycerol as by-product. The liquid-phase oxidation of glycerol with air on platinum catalysts was investigated to prepare valuable oxidation products such as glyceric acid or dihydroxyacetone. The effect of the pH (pH range 2–11) and of different metal catalysts was studied. The selectivity to glyceric acid can be as high as 70% at 100% conversion on Pd/C at pH 11. On Pt/C catalyst, glyceric acid was still the main product (55% selectivity); but the deposition of bismuth on platinum particles orientates the selectivity towards the oxidation of the secondary hydroxyl group to yield dihydroxyacetone with a selectivity of 50% at 70% conversion.

Selective oxidation with air on metal catalysts

Abstract Oxidation of organic molecules with air on metal catalysts has been known for a long time but there has been a renewed interest in recent years because these catalytic reactions are environmentally safe and could replace stoichiometric oxidations. This paper describes several oxidation reactions conducted either at high temperatures in the gas phase or at moderate temperatures in the liquid phase; in both cases they proceed via a mechanism of oxidative dehydrogenation on the metal surface. Ethylene glycol was converted to glyoxal at 550°C on Ag/SiC catalyst with a 70% yield provided promoters were added to the reaction feed (diethylphosphite or iodine) or deposited on the catalyst (LiPO4 or H3PO4). The promoters improve the conversion and selectivity by modifying the structure and the oxygen concentration on the surface of silver. Oxidation of glyoxal to glyoxylic acid, glucose to gluconic acid and glycerol to various oxygenated derivatives were conducted in water at 60°C in the presence of carbon-supported palladium or platinum catalysts. Bismuth promoter, deposited on the platinum metals by redox reaction, improves the catalyst activity by preventing over-oxidation of the metal surface and favors the oxidation of secondary alcohol functions into keto-derivatives. At higher reaction temperatures, platinum catalysts produce C-C bond rupture with the formation of carboxylic acids with smaller chains. Thus, cyclohexanol was converted into C6, C5, and C4 diacids with a 45% selectivity to adipic acid on Pt/C catalysts at 150°C.

Deactivation of metal catalysts in liquid phase organic reactions

The paper gives a general survey of the factors contributing to the deactivation of metal catalysts employed in liquid phase reactions for the synthesis of fine or intermediate chemicals. The main causes of catalyst deactivation are particle sintering, metal and support leaching, deposition of inactive metal layers or polymeric species, and poisoning by strongly adsorbed species. Weakly adsorbed species, poisons at low surface coverage and solvents, may act as selectivity promoters or modifiers. Three examples of long term stability studies carried out in trickle-bed reactor (glucose to sorbitol hydrogenation on Ru/C catalysts, hydroxypropanal to 1,3-propanediol hydrogenation on Ru/TiO2 catalysts, and wet air oxidation of paper pulp effluents on Ru/TiO2) are discussed.

Catalytic Conversion of Biomass: Challenges and Issues

There are strong incentives to develop the production of fuels, chemicals and materials from biomass. However, the extensive use of biomass for industrial production, particularly for biofuels which involves high tonnages, raises environmental and ethical issues that may throw some doubts on the sustainability of these processes. The processing cost of biomass must be decreased by designing new processing routes and catalytic systems because those employed for hydrocarbons are not adapted to the molecular structure of biomolecules. To avoid competition with food supply, lignocellulosic feedstocks should be used rather than traditional agricultural crops particularly for biofuel production. Life-cycle assessment, which takes into account all the inputs and outputs of a process/product, should be carried out to evaluate the environmental impact of processes and used as a decision-making tool for product development.

Glucose hydrogenation on promoted Raney-nickel catalysts

Glucose hydrogenation has been studied in a well stirred, high-pressure batch reactor on promoted Raney-nickel catalysts. Mo-, Cr-, and Fe-promoted catalysts were prepared by soda attack on Ni40-χAl60Mχ alloys. Sn-promoted catalysts were obtained by controlled surface reaction of Sn(Bu)4 on the hydrogen-covered surface of a Raney-nickel obtained from a Ni2Al3 alloy. The loading of tin is stoichiometric and its distribution on the nickel surface is very homogeneous down to nanometer scale. For an optimum promoter concentration the catalysts are up to seven times more active than unpromoted ones. A good distribution of the promoter in the catalyst grain is required to obtain the best rate enhancement; in the case of molybdenum this is obtained by annealing the alloys. The promoters in a low-valent state on the nickel surface act as Lewis adsorption sites for the oxygen atom of the carbonyl group which is then polarized and thus more easily hydrogenated via a nucleophilic attack on the carbon atom by hydride ions. The activities of Mo- and Cr-promoted catalysts decrease slightly after several recyclings in successive hydrogenation experiments. This is mostly due to surface poisoning by cracking products formed in side reactions. Fe- and Sn-promoted Raney-nickel catalysts deactivate very rapidly because Fe and Sn are leached away from the surface. Iron is washed to the liquid phase whereas tin remains in the Raney-nickel micropores.

Process options for converting renewable feedstocks to bioproducts

This paper discusses the relative advantages of different process options to convert renewable feedstocks (carbohydrates, vegetable oils, terpenes and lignocellulosic materials) into valuable chemicals and polymers. Three process options are considered: (1) via degraded molecules, (2) via platform molecules, (3) via one-pot processes. These routes can all be integrated in a biorefinery scheme which maximises the value derived from biomass. These process options are illustrated by selected examples underlining the green chemistry value of process options 2 and 3. Stress is laid on new value chains adapted to biomass composition and on the use of recyclable heterogeneous catalysts that lead to waste minimisation and decrease the processing cost of renewables.

X-ray diffraction study of cupric ion migrations in two Y-type zeolites containing adsorbed reagents

Abstract X-Ray diffraction study of two copper-exchanged Y zeolites (Cu 16 Na 24 Y and Cu 12 Na 5 H 27 Y) in the dehydrated state showed that the cupric ions strongly prefer S I sites in the sodalite cages where they are firmly bonded to three framework oxygen atoms. The effect of sorbed molecules on the cation distribution was studied by adding ammonia, pyridine, naphthalene and butene to the dehydrated zeolite. Adsorption of a small amount of ammonia which can enter the sodalite cages produced slight but significant changes in the copper position. Addition of pyridine, naphthalene or butene induced an important migration of copper ions from S I and S I sites to the supercages where they can interact with sorbed molecules. The nature of the cation-organic molecule associations was investigated: infrared measurements and X-ray results provided evidence of a proton transfer from the organometallic complexes to the framework oxygen atoms.

Chemioselectivity in the catalytic hydrogenation of cinnamaldehyde. Effect of metal particle morphology

The selectivity of platinum and rhodium catalysts for the hydrogenation of cinnamaldehyde into cinnamyl alcohol is much higher on large, facetted metal particles them on small (<3 nm) particles. This is attributed to a steric effect of the phenyl group which hampers the molecule to adsorb parallel to the flat metal surface thus favouring the adsorption and hydrogenation of the carbonyl group with respect to the C = C double bond.

Geometric and electronic effects in the selective hydrogenation of α,β-unsaturated aldehydes over zeolite-supported metals

Abstract The hydrogenation of two α, β-unsaturated aldehydes, cinnamaldehyde and 3-methylcrotonaldehyde was investigated over Ru, Pt, and Rh. The use of zeolite supports was compared with activated carbon for Ru, and the effect of changing the neutralizing cation in the Y zeolite was compared for all three metals. Selectivity to the unsaturated alcohol could be influenced by both geometric and electronic effects, and the relative importance of these effects was found to depend on the nature of the organic substrate.