Paolo Pollesel

A priori selection of shape-selective zeolite catalysts for the synthesis of 2,6-dimethylnaphthalene

Modeling tools based on molecular mechanics and molecular dynamics were used for selecting shape-selective zeolite catalysts for the synthesis of 2,6-dimethylnapthalene (2,6-DMN) through the alkylation of naphthalene (NAPH) or via isomerization of other DMN isomers. A number of medium- (MFI and EUO) and large-pore zeolites (∗BEA, MOR, MAZ, FAU, LTL, OFF, and MTW) were considered and for each of them the minimum energy pathways for the diffusion of naphthalene, 1- and 2-methylnapthalene (MNs), and 1,5-, 1,6-, 2,6-, and 2,7-dimethylnapthalene (DMNs) were computed. The results of the simulations indicated that the diffusion of MNs and DMNs isomers in the medium-pore zeolites is impeded by high-energy barriers, leading to the conclusion that this kind of structure can be used neither in the isomerization nor in the alkylation reaction. In contrast, large-pore zeolites are more promising though their behavior strongly depends on the effective size of the pore openings. Among them, MTW was predicted to be the most promising candidate for the selective alkylation of NAPH to 2,6-DMN. In fact, the simulations indicated high-energy diffusion barriers not only for molecules bearing a CH3 group in the α-position but also for the undesired 2,7-DMN molecule. Catalytic tests, performed in the presence of 1,2,4-trimethylbenzene as a solvent, confirmed the prediction since MTW gave the highest 2,6-DMN yields with a 2,6-/2,7-DMN ratio in the range 2.0–2.6, well above the thermodynamic value of ≈1 obtained with the other zeolites. The good catalytic performances of MTW were explained by the fact that, unique among the large-pore zeolites considered, this zeolite showed a better stabilization of the 1,1-diarylmethane intermediate molecules leading to 2-MN, 2,6-DMN, and 2,7-DMN. Their formation can be considered more probable than for those deriving from the electrophilic attack of the benzyl carbocation in the α-position of the naphthalene ring.

The role of MoS2 nano-slabs in the protection of solid cracking catalysts for the total conversion of heavy oils to good quality distillates

The total conversion of the oil barrel to good quality fuels and distillates has been an overriding goal in the oil refinery industry. Today, it is even more important to improve the effective use of the energy fossil reserves. The actual technologies still produce variable amounts of low quality fractions (e.g. fuel oil, bunker oil) or by-products (e.g. coke). The evolution of the slurry hydrocracking technology can open the way to achieve the objective. This technology was originally developed in Germany in the first half of the last century and reconsidered by several research groups in the past decades. The catalyst used in the slurry process is still constituted by the same materials developed by German scientists in the last century, i.e. bulk, crystalline, nano-sized iron, molybdenum or tungsten sulfide. We have demonstrated now that it is possible to improve the catalytic performances by combining the excellent hydrogenation, hydrodesulfurization and hydrodemetallation properties of dispersed MoS2 catalyst with those of a conventional cracking catalyst. This dual catalyst system demonstrates for the first time the ability of dispersed MoS2 particles to protect the cracking catalyst against rapid decay due to coke accumulation and metal poisoning.

TPD-TPR-MS mechanistic study of the synthesis of 2-methylpyrazine over palladized Zn-Cr oxide

Abstract A mechanistic study of the cyclization of ethylenediamine (ED) and propyleneglycol (PG) to 2-methylpyrazine is reported, carried out by means of the TPD-TPR-MS technique. The reacting system proved to be complex, due to the presence of numerous intermediates and by-products, deriving either from one of the two reactants, or from both. The optimal reaction temperature, permitting the best selectivity to the desired product, was about 660 K. At least two different types of surface sites are present on the catalyst, and only the higher-energy ones activated the reactants. The reaction probably involves a rate-determining step of the Rideal-Eley type, between adsorbed PG and ED coming from the gaseous phase. This step leads to a fully hydrogenated intermediate, 2-methylpiperazine, which quickly dehydrogenates and aromatizes to 2-methylpyrazine.

Heteropolyacids as effective catalysts to obtain zero sulfur diesel

This paper deals with the catalytic properties of different supported heteropolyacids (HPAs), both molybdenum- and tungsten-based, in the oxidative desulfurization process of diesel. We are jointly developing a new oxidative desulfurization process, aimed at reducing the sulfur content in diesel to less than 10 ppm (parts per million) using in situ produced peroxides. In this new process, high-molecular-weight organosulfur compounds, such as 4,6-dimethyl-dibenzothiophene (DMDBT), difficult to be eliminated by conventional hydrodesulfurization, are oxidized to the corresponding sulfones and subsequently removed by adsorption. Molybdenum-based HPAs, with Keggin structure, proved to be the most active and selective catalysts for oxidizing DMDBT with on-stream lifetimes exceeding 1500 h time on stream (t.o.s.).

Zeolite science and technology at Eni

In the last forty years Eni laboratories have contributed to the advancement of zeolite science and technology in both the synthesis and characterization of materials and their application in catalysis. This work has led to several industrial applications of zeolites, such as selective oxidation, acid–base catalysis, gas separation and water remediation. A brief review of the main results is reported with some comments on the future perspectives of this technology.

Coating method for Ni/MgAl2O4 deposition on metallic foams

Abstract A new method to deposit active washcoats of Ni/MgAl 2 O 4 steam-reforming catalysts over FeCrAlloy foams is reported in this work. The MgAl 2 O 4 powdered support was prepared via a co-precipitation method, and Ni was dry-impregnated on it. The deposition of the catalyst over the foams was performed by dip-coating followed by air-blowing (dip-blowing). The resulting washcoat layers were quite homogeneous and uniform, and well adherent to the metallic support. Prototype catalyst samples, tested at the lab-scale, were found to be active and selective in the steam reforming process.

New Method for H2S Removal in Acid Solutions

Several different technologies are available for H(2)S removal from the gas stream of medium capacity. Among them, the most widely used is Locat with more than 120 plants worldwide. In the last decade, many new processes, such as Sulfatreat-DO, Crystasulf, Caltech, and UCSR, were proposed to overcome the drawbacks of the state-of-the-art processes (low sulfur purity, chemical degradation, thiosulfate formation). We have developed a new H(2)S conversion method based on acid ferric nitrate solution, co-catalyzed by a heteropolyacid. H(2)S was converted to pure sulfur (>99.9 %), with no traces of organic compounds. Due to the acid pH of the solution, no chelant or surfactant was needed and iron content in the solution could reach very high levels. Keggin heteropolyacid (H(6)PW(9)V(3)O(40)) catalyzed the reoxidation of reduced ferrous solution with air at mild temperature and at very high reaction rate. The undesired side reaction (NO(x) formation) could be avoided by simply increasing the oxygen partial pressure.

Pd/La H-Y a novel and promising catalyst for hydrocracking of heavy Pygas

Environmental legislation will restrict the total aromatic content in gasoline. Consequently, the amount of heavy pyrolysis gasoline (a by-product from steam cracker, mainly composed of C 7 –C 9 aromatics) blended into motor gasoline will be limited. Hydrocracking into premium stream cracker feed has been suggested as a possible way to get value from pyrolysis gasoline. Pd/LaH-Y proved to be an effective catalyst not only in the hydrocracking of C 7 –C 9 aromatics, but also of polynuclear aromatics (e.g. naphtalenes). Feed with relevant sulphur content can be successfully hydrotreated too.