Dehydrogenative Coupling of Alkanes and Benzene Enhanced by Slurry-Phase Interparticle Hydrogen Transfer.

The dehydrogenative coupling reaction of alkanes and benzene has attracted attention as a method of direct conversion of alkanes to raw materials for useful chemical products. Here, we report the first combined catalyst system composed of hydrotalcite-supported palladium and solid acid aluminum-exchanged montmorillonite for the direct alkylation of benzene promoted by slurry-phase interparticle hydrogen transfer at 150 °C. The combination of the two catalytic particles showed excellent activity and achieved the maximum benzene conversion of 21% and target product selectivity of 84% in the reaction of n-heptane and benzene. Our results, thus, provide a feasible strategy to design efficient liquid-phase reaction systems employing simple physical mixing of two catalytic particles.

Direct Alkylation of Benzene at Lower Temperatures in the Liquid Phase: Catalysis by Montmorillonites as Noble-Metal-Free Solid Acids.

Alkylated benzenes are widely used as raw materials for the production of a variety of chemical compounds. Conventionally, they are obtained by the Friedel-Crafts reaction between alkyl halides and benzene. In this study, the synthesis of halogen-free alkylated benzenes was made possible by the direct alkylation of benzene with alkanes using montmorillonites as noble-metal-free solid acid catalysts. The direct alkylation of benzene with n-heptane was performed at 150 °C. Aluminum-exchanged montmorillonite showed the highest yield of the target C-7 alkylated products (Ph-C7) compared with other homogeneous and heterogeneous acid catalysts: 1.8 % conversion of benzene with 58 % selectivity in 16 h. The montmorillonite catalyst system was applied to other linear and cyclic alkanes to give the corresponding alkylated products with good selectivities.

Determination of the positions of aluminum atoms introduced into SSZ-35 and the catalytic properties of the generated Brønsted acid sites.

The positions of aluminum (Al) atoms in SSZ-35 together with the characteristics of the generated protons were investigated by 27Al multiple quantum magic-angle spinning (MQ-MAS), 29Si MAS, and 1H MAS NMR data analyses accompanied by a variable temperature 1H MAS NMR analysis. The origin of the acidic -OH groups (Brønsted acid sites) generated by introducing Al atoms into the T sites was investigated and the T sites introduced into the Al atoms were revealed. To further determine the catalytic properties of the acidic protons generated in SSZ-35, the influence of the concentration of the Al atoms on the catalytic activity and selectivity during the transformation of toluene was examined.

Experimental and computational studies of the roles of MgO and Zn in talc for the selective formation of 1,3-butadiene in the conversion of ethanol.

The one-step conversion of ethanol to 1,3-butadiene was performed using talc containing Zn (talc/Zn) as a catalyst. The influence of the MgO and Zn in the talc on the formation rate and selectivity for 1,3-butadiene were investigated. MgO as a catalyst afforded 1,3-butadiene with a selectivity that was nearly the same as talc/Zn at ∼40% ethanol conversion at 673 K, although the rate of 1,3-butadiene formation over MgO was about 40 times lower than that over the talc/Zn. The introduced Zn cations were located in octahedral sites in place of Mg cations in the talc lattice. The Zn cations accelerated the rate of CH3CHO formation from ethanol, resulting in an increase in the rate of 1,3-butadiene formation. However, the rate of CH3CHO consumption to form crotonaldehyde was not influenced by Zn, although the distribution of crotonaldehyde was decreased with increasing Zn concentrations. X-ray photoelectron spectra of talc/Zn showed that the O1s binding energy was increased by increasing the concentration of Zn, while those of both Mg2p and Si2p were hardly influenced. DFT calculations were used to estimate the atomic charges on the O, Mg, Si, and Zn atoms when an atom of Zn per unit cell of talc was introduced into an octahedral site. On the basis of the results for the conversion of ethanol into 1,3-butadiene and the corresponding DFT calculations, the roles of the O, Zn, Mg, and Si atoms in the talc catalyst for the formation of 1,3-butadiene from ethanol were discussed.

Mechanistic Insight into a Sugar-Accelerated Tin-Catalyzed Cascade Synthesis of α-Hydroxy-γ-butyrolactone from Formaldehyde.

Applications of the formose reaction, which involves the formation of sugars from formaldehyde, have previously been confined to the selective synthesis of unprotected sugars. Herein, it is demonstrated that α-hydroxy-γ-butyrolactone (HBL), which is one of the most important intermediates in pharmaceutical syntheses, can be produced from paraformaldehyde. In the developed reaction system, homogeneous tin chloride exhibits high catalytic activity and the addition of mono- and disaccharides accelerates the formation of HBL. These observations suggest that the formose reaction may serve as a feasible pathway for the synthesis of important chemicals.

Mechanistic studies on the cascade conversion of 1,3-dihydroxyacetone and formaldehyde into α-hydroxy-γ-butyrolactone.

The chemical synthesis of commercially and industrially important products from biomass-derived sugars is absolutely vital to establish biomass utilization as a sustainable alternative source of chemical starting materials. α-Hydroxy-γ-butyrolactone is a useful synthetic intermediate in pharmaceutical chemistry, and so novel biomass-related routes for its production may help to validate this eco-friendly methodology. Herein, we report the specific catalytic activity of homogeneous tin halides to convert the biomass-derived triose sugar 1,3-dihydroxyacetone and formaldehyde into α-hydroxy-γ-butyrolactone. A detailed screening of catalysts showed the suitability of tin catalysts for this reaction system, and isotope experiments using [D2]paraformaldehyde, substrate screening, and time profile measurements allowed us to propose a detailed reaction pathway. In addition, to elucidate the activated species in this cascade reaction, the effect of additional water and the influence of additional Brønsted acids on the reaction preferences for the formation of α-hydroxy-γ-butyrolactone, lactic acid, and vinyl glycolate were investigated. The active form of the Sn catalyst was investigated by (119)Sn NMR spectroscopy.

Tin-catalyzed conversion of biomass-derived triose sugar and formaldehyde to α-hydroxy-γ-butyrolactone.

The direct conversion of biomass-derived 1,3-dihydroxyacetone (DHA) and formaldehyde to α-hydroxy-γ-butyrolactone (HBL) was achieved through the use of tin(iv) chloride and a small amount of water and the yield reached up to 70%. The reaction mechanism was also investigated by incorporating d2-formaldehyde into the reaction mixtures.

Influence of Si distribution in framework of SAPO-34 and its particle size on propylene selectivity and production rate for conversion of ethylene to propylene.

To investigate the effect of SAPO-34 particle size (with a fixed Si mole fraction in its framework) and that of the Si mole fraction (in a SAPO-34 framework with fixed particle size) on propylene selectivity and production rate for the conversion of ethylene to propylene, SAPO-34 was prepared by hydrothermal synthesis using tetraethyl ammonium hydroxide or morpholine as a structural agent. The conversion of ethylene was carried out at 473 K using SAPO-34. The selectivity for propylene, the rate of propylene production, and the lifetime of the catalyst were strongly influenced by the catalyst crystal size. The SAPO-34 with a approximately 2.5 microm particle size had the highest selectivity for propylene (approximately 80%) up to a high conversion of ethylene (approximately 70%), while SAPO-34 with smaller particles had a longer catalyst lifetime, implying that catalyst deactivation was suppressed. The mole fraction of Si in the SAPO-34 framework with fixed particle size had little influence on the selectivity for propylene, indicating that the acid strength of SAPO-34 is independent of the Si mole fraction and all protons in SAPO-34 behave equivalently. Furthermore, the acid strength of protons determined by the measurements of NH(3)-TPD (temperature-programmed desorption) spectra did not depend on either the Si mole fraction or the SAPO-34 particle size. This result was also evident in the cracking rate of n-butane, which increased proportionally with increasing number of protons in SAPO-34.The number of protons generated by the incorporation of Si4+ into the SAPO-34 lattice increased proportionally, up to one Si atom introduced into every cage of SAPO-34, but did not continue to increase with further introduction of Si4+ into the lattice.