Giuseppe Bellussi

Synthesis of propylene oxide from propylene and hydrogen peroxide catalyzed by titanium silicalite

Abstract The epoxidation of propylene with hydrogen peroxide in the liquid phase, in the presence of titanium silicalite catalyst (TS-1), is described. The best solvents are methanol and methanol/ water mixtures. The temperature is normally between room temperature and 60°C. Under these conditions, reaction rates are fast, yields on H2O2 are quantitative, and selectivity to propylene oxide is very high. Propylene glycol and its monomethyl ethers and trace amounts of formaldehyde are the only by-products formed. Selectivity is further improved and the hydrolysis of the epoxide is almost suppressed when the residual acidity of the catalyst is completely neutralized. The activity of spent catalyst is recovered by calcining at 550°C or, more simply, by washing with solvents. Complete activity recovery shows that Ti is not removed from the crystalline framework during the epoxidation reactions.

Reactions of titanium silicalite with protic molecules and hydrogen peroxide

The properties of titanium silicalite (TS-1) in reactions with water, hydrogen peroxide, and alcohol molecules have been studied by means of IR and NMR spectroscopy, and acid activity tests. An IR absorption is shown by TS-1 in the region 900–975 cm−1. Its exact position depends on the amount of adsorbed water, on exchange reactions with 17O- and 18O-labeled water, and on the average size of the crystallites. In 17O MAS NMR spectra a peak is shown at σ 360 ppm from H2 17O (σ = 0). IR and NMR spectra are discussed and interpreted in terms of Ti sites as constituted by tetrahedral [TiO4] units. TiOSi bonds react with water at near room temperature, producing TiOH and SiOH species. Reactions with hydrogen peroxide produce acidic derivatives, which catalyze the hydrolysis of cis and trans 2,3-epoxybutane in methanol, ethanol, and aqueous media. A five-membered ring hydrogen bonded structure, in which a titanium hydroperoxo moiety, TiOOH, and a protic molecule, ROH (R = H, CH3, C2H5), are involved, is proposed for these species. Their possible role in selective oxidations of hydrocarbons is discussed.

Production of titanium containing molecular sieves and their application in catalysis

Abstract This paper reviews several important issues related with industrial application of catalysts based on titanium silicalite-1 (TS-1). The catalyst preparation has been discussed, especially considering the most critical parameters for industrial application. Two processes already demonstrated on industrial scale (phenol hydroxylation and cyclohexanone ammoximation), and a process, under development by several industrial groups (propylene epoxidation), have been reported and discussed. The possibility to insert titanium in large pore zeolites, in order to widen the application field of this kind of materials, has been considered and the behaviour of several new materials has been reported and compared with the catalytic properties of TS-1.

Layered structure of ERB-1 microporous borosilicate precursor and its intercalation properties towards polar molecules

Abstract As-synthesized ERB-1 borosilicate has a bi-dimensional layered structure, and the three-dimensional (3D) microporous structure is formed after calcination at 270°C. X-Ray powder diffraction (XRD), temperature-programmed desorption (TPD) and 29 Si magic-angle spinning nuclear magnetic resonance (MAS NMR) analyses demonstrated that the formation of the 3D ordered structure occurs through the condensation of silanol groups present on the surfaces of the layers. As-synthesized ERB-1 displays intercalation properties towards polar molecules such as ethylene glycol, isopropanol and [2,2,2]-azabicyclooctane.

Mesoporous silica-aluminas as catalysts for the alkylation of aromatic hydrocarbons with olefins

Abstract Two amorphous mesoporous silica-aluminas (MSA and MCM-41) are compared with the amorphous microporous silica-alumina (ERS-8) and the zeolite beta in the liquid-phase alkylation of toluene with propylene. The catalytic activity, the selectivity to o-, m- and p-cymenes and the formation of polyalkylates are discussed as a function of acidity and porosity. The catalytic behaviour of MSA, MCM-41, ERS-8 and zeolite beta is also compared with data reported in the literature for traditional alkylation catalysts (AlCl3–HCl and supported phosphoric acid, SPA) and for other acidic zeolites. MSA and MCM-41 show alkylation activities comparable with zeolite beta, while their isomerization and transalkylation activities are lower than those of zeolite beta and AlCl3–HCl, but similar to SPA. Such behaviour is in agreement with the Bronsted acidity of the materials studied.

Experimental and computational study of beta, ZSM-12, Y, mordenite and ERB-1 in cumene synthesis

The catalytic performance of zeolite β in the liquid phase alkylation of benzene with propylene is compared with that of other zeolites: MOR, ERB-1, USY, MTW. The comparison is carried out both by catalytic tests and by computational evaluation of the energy barriers for diffusion of the product molecules and of the binding energies (BEs) of the same molecules, inside the zeolite pores. Among the zeolites studied, zeolite β appears to be one of the most efficient catalysts, producing the smallest amount of propylene oligomers and of n-propylbenzene. The energy diffusion barriers and the BEs, both calculated for cumene and DIPB isomers account for the outstanding performance of zeolite β.

New trends in the synthesis of crystalline microporous materials

Zeolites and related microporous materials form the most important class of microporous solids due to their practical importance in different technological areas. In spite of the extensive research carried out in previous decades, it is surprising to realize that there is still space for innovation in this area, making microporous crystalline solids special among all classes of materials known today. We illustrate here the most recent advances in the field, focusing on the research topics that, in our opinion, are most likely to provide results of practical interest. Three main topics are discussed: (1) the synthesis of new framework topologies, with particular attention to those having extra-large and/or multidimensional pore systems; (2) the modification of the morphological and textural properties of known zeolites, including the discussion on two-dimensional structures and on the synthesis of nanocrystals and of the hierarchical porous structures; (3) the still poorly explored field of silica-based hybrid organic–inorganic porous crystalline materials (hybrid zeolites). For each of these topics, a selection of the most relevant results reported in the literature is provided together with some considerations on the potentialities and future perspectives.

Industrial Catalytic Aspects of the Synthesis of Monomers for Nylon Production

The industrial production of the monomers used for the preparation of polyamides (e.g. nylons) has undergone significant innovation. Since the last decade novel technologies have been developed, based on new catalysts that are more efficient, safe and environmentally friendly. Several new plants using new catalytic technologies have come on stream recently. Other technologies are close to industrial demonstration. What is pushing this change? What challenges occurred and what was the contribution of heterogeneous catalysis? Which other problems are still to be solved? In this article we will address all these questions.

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.

Selective catalytic reduction of NOx by propane on Co-loaded zeolites

Abstract To ascertain the reason of the superiority of cobalt ion-exchanged BEA (Co-BEA) in the selective catalytic reduction of NOx by hydrocarbons (HC-SCR) using propane, the dependence of the catalytic performance of Co-loaded zeolite (Co-zeolite) in the HC-SCR reaction using propane on zeolite species was examined using IR and catalytic activity tests. The order of catalysts according to their initial activity in the absence of sulfur dioxide (SO2) was BEA>MFI>MOR≫FER≫FAU. In the presence of SO2, only Co-BEA exhibited stable activity, whereas the activities of Co-MOR and Co-MFI rapidly decreased, although no tendency to clogging of micropores nor decrease in dispersion of Co were observed. On the other hand, there was no obvious difference in the IR spectra of adsorbed NOx species between Co-BEA and Co-MFI. Since in the presence of SO2 the crystal size effect on catalytic performance was observed even with Co-BEA, intracrystalline diffusion is considered to control the overall reaction rate under such conditions. Thus, it is concluded that the micropore structure of BEA, advantageous to intracrystalline diffusion, is considered to be one of the reasons for the superiority of Co-BEA in the HC-SCR reaction using propane.