Carlo Lucarelli

Vapor phase Beckmann rearrangement using high silica zeolite catalyst

Vapor phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam has been studied using high silica zeolite catalysts. Catalysts with different crystal sizes and gel-ageing times have been activated by ionic exchange in different conditions by means of a highly basic solution and a nearly neutral solution both containing ammonium salts. Samples have been calcined at different temperatures in order modify the number of defective sites. We observed that samples exchanged by means of a highly basic solution (pH > 10) and calcined at a relatively lower temperature (450 °C) show the most interesting catalytic results. X-ray powder diffraction patterns of these samples show retention of the unit cell symmetry (orthorhombic cell) if compared to the dried sample. NH3-TPD confirms the low acidity of high silica zeolites, however a higher amount of desorbed ammonia is observed for the samples exchanged at higher pH and calcined at 450 °C. Due to silanol nests the IR spectra of the same samples show the formation of Si–NH2 bonds which are absent in the same material exchanged by other methods. Such sites seem to promote the high stability of the high silica zeolite catalysts also to the regeneration which is needed to remove the heavy carbonaceous compounds from the catalyst surface.

Examples of heterogeneous catalytic processes for fine chemistry

Fine chemicals are highly pure substances that are commercially produced by chemical reactions for highly specialized applications. In most cases, however, these reactions involve stoichiometric and highly polluting steps. A possible solution is the development of processes using enzymatic, homogeneous or heterogeneous catalysts. In this review, selected examples of clean heterogeneously-catalyzed reactions applied to the synthesis of fine chemicals are reported for the purpose of highlighting the growing need for more sustainable industrial processes, i.e., processes that produce minimal waste and avoid as much as possible the use of toxic and/or hazardous reagents and solvents. A thorough knowledge of catalyst properties, reaction conditions and interactions with the reacting substrate are essential for optimizing the synthesis, thus making it possible to move on from laboratory to industrial production.

Vanadium and niobium mixed-oxide catalysts obtained via sol-gel: preparation and catalytic behaviour in oxidative dehydrogenation of propane

Publisher Summary This chapter focuses on the optimization of the hydrolytic sol–gel preparation method achieving the highest possible control of the molecular scale interdispersion of the mixed-oxide phases. More particularly, the effects of various promoters and higher Nb/V ratio on the hydrolytic sol–gel preparation are investigated. The possible relationship between the nature and interdispersion of the oxide phases present in the Nb–V systems, and the resulting catalytic performances in the oxidative dehydrogenation (ODH) of propane are presented. The sol–gel preparation of the 1:1 Nb/V systems led to the formation of gelatinous precipitates with the only exception of the sample obtained by adding citric acid as promoter, which turned into a gel. The sol–gel preparation of 4.5:1 and 9:1 Nb/V systems led in both cases to the formation of yellow coloured gels. From these preliminary results, it was concluded that a high Nb amount or the presence of a V complexing agent such as citric acid are necessary conditions for preparing Nb/V mixed gels, otherwise the solution of Nb and V precursors is not stable upon water addition, and a yellow gelatinous precipitate readily forms, independently of the water amount and/or the precursors concentration adopted.

Exploiting H-transfer as a tool for the catalytic reduction of bio-based building blocks: the gas-phase production of 2-methylfurfural using a FeVO4 catalyst

Over the past decade, a great deal of effort has been devoted to developing reductive processes in the field of biomass valorisation for the sustainable production of bio-fuel additives and chemicals. Catalytic transfer hydrogenation, which uses alcohol as the hydrogen source, is an interesting approach that avoids the use of both high H2 pressure and precious metal catalysts. In this work, the vapour-phase production of 2-methylfuran from biomass-derived furfural (FU), using methanol as the H-transfer agent and FeVO4 catalyst, was studied. At a temperature of 320 °C it was possible to achieve 80% yield of 2-methylfuran, with small amounts of 2,5-dimethylfuran and 2-vinylfuran as by-products. Catalyst characterization highlighted that FeVO4 reduction took place under the studied conditions, leading to the in situ development of a true active phase. The study of the reaction network permitted us to infer on the relative contribution of H-transfer and hydrogenation, the latter from the in situ generated formaldehyde and H2, to 2-methylfuran, formation. The reported results indicate the potential application of H-transfer with FeVO4 catalysts as an efficient process for the selective de-oxygenation of biomass-derived molecules.

Sol-gel synthesis and characterization of Nb-Mo and Nb-Mo-V mixed oxides as catalysts for the selective oxidation of propane (poster)

In this work a modified hydrolytic sol-gel technique has been applied to synthesize binary and ternary systems based on Nb, Mo and V, as potential catalysts for the selective oxidation of propane to acrolein and/or acrylic acid. Crystalline mixed oxide phases were obtained and investigated by XRD, Raman and UV-VIS spectroscopy.

Effect of exchange procedure and crystal size on high silica MFI zeolite as catalyst for vapor phase Beckmann rearrangement

Abstract Caprolactam is the starting monomer for the production of Nylon-6 fibers and resins. The current caprolactam manufacturing process is energy intensive and generates considerable wastes (ammonium sulphate). For this reason, alternative paths for the production of caprolactam providing few-step cost effective production and environmentally friendly process are required. In year 2000 Sumitomo Inc. announced the build-up of a demonstration plant for the production of caprolactam.. This process allows an ammonium sulphate-free caprolactam manufacture and will result in an industrial plant by the end of year 2003. In a recent paper Ichihashi et al. [1]claimed long-time catalytic tests with a high silica MFI zeolite which is rather active and selective towards caprolactam production. In this paper we report a study on the effect of catalyst activation method and acid sites distribution on caprolactam selectivity of high silica MFI zeolites of different crystal size. We found that catalysts activation by a NH4NO3 alkaline solution and calcinations at 450°C promotes structural rearrangement of silicalite-1 unit cell and catalytic performances remarkably higher than other silicalite-1 activated by other methods. In addition we show the direct correlation between caprolactam selectivity and H-bonded (nests of silanols and vicinal silanols) distribution.

Insights into the Reactivity of Thiophene: Heterogeneous Alkylation

The importance of thiophene derivatives in the fine chemical industry lies in the use of this class of molecules as raw materials in the synthesis of drugs, fragrances and pesticides. Nowadays, the synthesis of these molecules is multistep and expensive. The gas phase alkylation of thiophene on solid acid catalysts has been deeply studied by focusing on the possibility to control the product distribution of the reaction, paying particular attention to the relative amount of the 2- and 3-alkylthiophene, kinetic and thermodynamic products respectively. The difficulties in changing the 2:3 isomer ratio have been justified through the comprehension of thiophene behavior on the catalyst surface, that is responsible for the complex adsorption/desorption phenomena. It has been showed that the reaction is mainly affected by the strong adsorption of thiophene on the catalytic sites, with the critical step of the reaction represented by the saturation of the catalyst surface.

Novel thiotolerant catalysts for the on-board partial dehydrogenation of jet fuels

The possibility of producing on-board H2 by dehydrogenation of petrol derivates is interesting for transport applications. Traditional Pt–Sn systems, however, cannot be used without purifying the fuel from its sulphur content, and the dehydrogenation reaction consumes energy owing to its endothermic nature. To limit the energy demand for the entire process, it is necessary to eliminate the need for any reactant purification step, thus feeding the real fuel without desulphurization. In this respect, Ni- and Co-based catalysts capable of working under hydrodesulphurization conditions answered such demand, allowing them to carry out the reaction in the presence of sulphurated organic substrates. Tests conducted on nickel and cobalt phosphides, as prepared from the corresponding dihydrogenphosphite by temperature programmed reduction and supported on silica Cab-osil, indicated these materials as very active catalysts capable of producing 1500 N l per h per kgCAT of H2 after 24 h of reaction in the presence of 50 ppm of sulfur. These catalysts remained active and stable even when 250–500 ppm of sulphur was introduced in the feed.