Pietro Moggi

Mixed-oxide catalysts involving V, Nb and Si obtained by a non-hydrolytic sol-gel route : preparation and catalytic behaviour in oxydative dehydrogenation of propane

Abstract One-step non-hydrolytic condensation reactions, starting from VO(O i Pr) 3 and NbCl 5 , have been used for the first time to prepare Nb-V oxide catalysts. Different materials containing the NbVO 5 phase at different purity levels have been obtained, after thermal treatments, depending on the experimental conditions. The synthetic procedure has also been applied to prepare ternary Nb-V-Si oxide systems. From preliminary catalytic reaction studies it appears that the catalysts so prepared are promising with respect to their interesting performances in the oxidative dehydrogenation (ODH) of propane. It has also been found that α-Sb 2 O 4 , physically blended with the Nb-V oxide materials, could act as an appropriate promoter to improve the catalytic performances of these systems.

Ruthenium cluster-derived catalysts for ammonia synthesis

Abstract Ruthenium supported on γ-alumina modified with KOH was tested as catalyst for ammonia synthesis under atmospheric pressure. Ru3(CO)12 and RuCl3 were compared as ruthenium precursors. The catalysts derived from Ru3(CO)12 exhibited an up to five times higher productivity than the corresponding ones derived from RuCl3. Ruthenium metal dispersion, which probably influences the catalytic activity, was measured both by carbon monoxide and hydrogen chemisorption tests, and observed by high resolution transmission electron microscopy (HRTEM), and was clearly higher in the case of the ruthenium cluster. Different ruthenium catalysts, with 2, 5, 8 and 10% metal and 30% potassium (added as KOH) on alumina, were prepared from Ru3(CO)12. The highest hourly productivity of ammonia, both referred to unit mass of the catalyst and to the ruthenium atom content, was obtained with 8% Ru/Al2O3 KOH at 623 K and atmospheric pressure.

Methyl methacrylate by gas phase catalytic condensation of formaldehyde with methyl propionate

Abstract The gas phase catalytic condensation of formaldehyde with methyl propionate to methyl methacrylate over niobium, tantalum or tungsten oxide catalysts by feeding formaldehyde as hemiformal or trioxane has been studied. Experiments were carried out over a wide range of reaction temperatures, contact times and reagent molar ratios to find the most favourable conditions for high methyl methacrylate yields and selectivities. The best results were obtained over: a) the niobium oxide catalyst by feeding formaldehyde as hemiformal and b) the tungsten oxide catalyst by feeding formaldehyde as trioxane. The influence of the formaldehyde source on the reaction products and the mechanism of the catalysis are also discussed.

Ru/MgO sol-gel prepared catalysts for ammonia synthesis

A new method of preparation of alkali-promoted Ru/MgO catalysts, based on a sol-gel procedure, starting from magnesium ethoxide, Ru3(CO)12 and a cesium compound has been designed. The gels were subjected to an activation/reduction procedure to substantially obtain Ru-CsOH/MgO. The activated catalysts were tested in ammonia synthesis at atmospheric pressure. It was clear that the sol-gel prepared Cs-promoted Ru/MgO catalysts are much more active, under the same reaction conditions, than the analogous catalysts prepared by impregnation procedures.

Fischer-Tropsch synthesis on alumina-supported ruthenium catalysts II. Influence of morphological factors

Abstract A Ru/γ-Al 2 O 3 (0.87% wt./wt.) catalyst has been studied for the Fischer-Tropsch synthesis (FTS) at 5 · 10 3 Pa, 508 K with a H 2 /CO ratio of 2/1. The same catalyst was also sintered at 973 K for different times in order to change the metal dispersion D M of Ru ( D M from 18 to 93%). The aim of the present work is to verify which atoms of Ru crystallites are most active in FTS. For this study a ‘model’ of truncated hexagonal bipyramid for the crystalline agglomerates has been assumed. It was verified that atoms with higher nearest neighbors i ( i ,8 and 9) on flat faces and edges are more active than those on vertexes and edges at lower i values ( i ,5 to 7). We found that larger crystallites decompose CO more easily than smaller ones, and that the turnover number for CO disappearance and for CH 4 , C2, C3, C5–C15 formation does not depend strongly on metal dispersion. However, on the contrary, we found that light olefins (C2 and C3) are easily formed on large crystallites. The above findings reveal that FTS could be considered as a structure sensitive reaction for the initial step, but are structure insensitive for the overall reaction.

Supported (η-C5H5)NiOs3(CO)9(μ-H)3 as a hydrogenation catalyst. Methanation of carbon monoxide and dioxide at atmospheric pressure

Abstract The title complex, supported on γ-alumina has been shown to be a very efficient catalyst for the hydrogenation of a variety of substrates; in particular its use permits high-efficiency methanation of CO and CO 2 at atmospheric pressure.

Gas phase aldol condensation of n-butyraldehyde to 2-ethylhexenal

Abstract Aldol condensation of n-butyraldehyde to produce 2-ethylhexenal in gas-phase over solid catalysts based on niobium, tantalum or tungsten oxide supported on silica was studied. The catalysts were prepared by different procedures based on co-precipitation or impregnation methods and characterized by X-ray fluorescence, scanning electron microscopy and specific surface-area determinations. The self-condensation of n-butyraldehyde in the temperature range 150-350°C, at contact times of 1-8 s, and through a continuous-flow microreactor at atmospheric pressure, was investigated. Supported niobium oxide, either co-precipitated or impregnated, gave better yields than both tantalum and tungsten oxide, with selectivities to 2-ethylhexenal higher than 95% up to 250°C. The performances of the niobium oxide-supported catalyst were also much better than those hitherto stated in the literature for a catalyst based on reduced tin supported on silica gel.

Co/SiO2 sol-gel catalysts for Fischer-Tropsch synthesis

Six catalysts with a different cobalt content were prepared following the sol–gel method. The samples were tested by the Fischer–Tropsch synthesis performed both at low and high temperature and pressure. All the catalytic performances are well correlated with the characterization results which highlighted the good metal distribution and the presence of a large amount of metallic cobalt (but not the whole) on the surface of both 10 and 30% Co catalysts. As a result, high CO conversions were observed with a particular sensitivity to the reaction pressure and also the limitation of the produced hydrocarbons fraction to C6 or C9 at low or high pressure, respectively.

Sol-gel preparation of pure and silica-dispersed vanadium and niobium catalysts active in oxidative dehydrogenation of propane

Hydrolytic and non-hydrolytic sol-gel routes are implemented to prepare various pure and silica-dispersed vanadium- or niobium-based oxide catalysts corresponding to the compositions Nb-V, Sb-V and Nb-V-M (M = Sb, Mo, Si). Starting reagents in the hydrolytic procedure are isopropanol solutions of the metal alkoxides. The non-hydrolytic route is based on reactions between metal and Si alkoxides and hexane suspensions of niobium(V) chloride. The catalysts are tested in propane oxidative dehydrogenation. NbVO5, SbVO4 and Nb2Mo3O11 are the major crystalline phases detected in the fresh catalysts, but structural modifications are in some cases observed after the use in the catalytic tests. At 500degreesC, propane conversions of 30% and selectivities to propene between 20 and 40% are attained. When the space velocity is decreased, acrolein is in some cases found as by-product.

Production of Ni-Ru bimetallic catalysts and materials by thermal and chemical decomposition of a tetranuclear bimetallic carbonyl cluster

Abstract The tetrahedral heterobimetallic cluster (C 5 H 5 )NiRu 3 H 3 (CO) 9 , 1 , when decomposed on KOH-modified γ-alumina, produces an effective heterogeneous catalyst for ammonia synthesis. Bimetallic particles have been evidenced on the support surface by analytical electron microscopy; their main size is 4.0 nm and their Ni/Ru atomic ratio is practically the same as that of the starting cluster. The treatment of unsupported 1 with alcoholic KOH gives a black, conductive, amorphous alloy powder. In this case, the ultrafine and bimetallic nature of the individual particles was also revealed by analytical TEM investigations.