Vol 56, No 3 (2016)

The review summarizes and analyzes the results of research in the field of triptane synthesis from methanol and dimethyl ether (DME). The reaction with a fairly high triptane yield occurs in the presence of both homogeneous and heterogeneous catalysts. It has been shown that InI₃ and ZnI₂ are the most commonly used catalysts for the homogeneous process, while zeolite systems based on H-BEA and H-Y are promising catalysts for the heterogeneous process. The effect of the catalyst nature (acidity and structure) on the type of resulting intermediates and the reaction mechanism has been described. Currently available approaches to describing the kinetics of the complex triptane synthesis reaction and the engineering aspects of the process have been discussed.

The preparation of N-methylaniline in two various processes: alkylation of aniline with methanol and hydroalkylation of nitrobenzene with methanol has been studied. Bifunctional molecular sieves containing metal copper as the hydrogenating component and zeolites BEA, MOR, MFI, FAU (Y) and mesoporous material MCM-41 as an alkylating component were used as catalysts. It has been shown that the modification of samples with copper nitrate increases the number of Lewis acid sites and decreases the number of Brønsted acid sites as copper embeds into cation exchange positions. It has been determined that the catalyst modification with copper increases the activity and enhances the selectivity towards N-alkylated products.

Effect of the type of active site on the catalytic properties of microporous crystalline silicoaluminophosphates with AEI structure synthesized at 150, 170, and 190°C has been investigated. The state of the active site was changed by varying the catalyst synthesis conditions. It has been established that during the synthesis of silicoaluminophosphates with the AEI structure from the reaction mixture of the same composition, an increase in the temperature and crystallization time leads to an increase of the silicon content and crystal size growth. The observed changes in the physicochemical properties are accompanied by the change of the silicon state in the structure of silicoaluminophosphates with the predominant formation of silicon “islands” via the SM3 mechanism. According to ²⁹Si NMR data, the formation of active sites of silicoaluminophosphates via the SM2 mechanism in the form of isolated silicon atoms in the structure is also observed for these materials. The presence of such sites, along with the morphological features of the crystals, determines the unusual catalytic properties of silicoaluminophosphate with AEI structure in MTO process, which are a high ethylene yield up to 41 wt % at an ethylene: propylene molar ratio of 1: 6.

2,3-Butanediol as a product of biomass processing is a cheap alternative raw material for synthesis of methyl ethyl ketone (MEK) and butadiene-1,3. The catalytic activity of Al- and Zr-containing BEA zeolites and an alumina-based catalyst in 2,3-butanediol dehydration has been investigated. It has been shown that the presence of Brönsted (H-BEA) or Lewis (Al₂O₃) sites leads to the selective formation of MEK and the combination of two types of sites (Zr-BEA) facilitates the formation of heavy products of condensation.

Silicoaluminophosphates with the ATO structure have been synthesized using two types of silicon source (metakaolin and silica sol). To determine the composition, morphology, and acid properties, SAPO-31 samples have been characterized by various methods. It has been found that the samples synthesized using different silica sources have very different properties. Samples of SAPO-31 synthesized with metakaolin have a higher acidity and are more active in the catalytic hydroisomerization of n-decane as compared with their counterparts prepared with silica sol. The difference in the effect of the type of silicon source has been explained by morphological features of silica particles formed during the dissolution of silicon source (spherical particles of a ~10 nm size in the case of silica sol and nanoplates of a ~1 nm size in the case of metakaolin). On the basis of data on the enhancement of acidic properties in the SAPO-31 samples with an increase in silicon concentration therein, it has been doubted that the SM3 mechanism of incorporation of Si atoms into the aluminophosphate ATO framework really operates (in any of its form). It has been shown that the SM2 mechanism alone operates instead, involving the independent formation of regions with an aluminosilicate composition.

The experimental data have been considered to match the theoretical mechanisms proposed previously to describe processes of oxidative carbonylation of methanol on copper-containing catalysts. The schemes examined cover methoxy intermediates, carbomethoxy intermediates, carbonates, and Cu(OCH₃)₂Cu binuclear clusters. The attack of the first methanol molecule on copper carbonate has been simulated in terms of the isolated cluster (8R) model with periodic boundary conditions (on CuMOR zeolite), and parameters of the individual steps involving description of the transition states have been evaluated.

The role of zeolite in transformations of hydrocarbons produced from CO and H₂ over a Fischer–Tropsch cobalt catalyst under the conditions of multibed arrangement of the cobalt catalyst and the zeolite has been determined. Hydrocarbon conversion over the HBeta zeolite occurs via the bimolecular mechanism, as evidenced by a low methane yield and a high yield of unsaturated gaseous and liquid hydrocarbons. The conversion over the CaA zeolite obeys the unimolecular mechanism, as evidenced by the formation of increased amounts of methane and saturated gaseous C₂–C₄ hydrocarbons.