Present health and daily life rely on synthetic materials such as pharmaceuticals, fine chemicals, synthetic fibers, and plastics, which are mainly produced by multi-step chemical conversions of petroleum products. However, the current standards of chemical synthesis need to be much improved. Oxidation is a core technology for converting petroleum-based materials to useful chemicals in higher oxidation states. Aqueous hydrogen peroxide is an ideal oxidant, because the atom efficiency is excellent and water is the only theoretical side product. A catalytic system consisting of ternary catalyst (tungsten complex, phase transfer catalyst, and phosphonic acid) allowed epoxidation of various olefins using aqueous 30 % hydrogen peroxide without any organic solvent. Palladium catalysts were also very effective for oxidation of α,β-unsaturated aldehydes to the corresponding acids under mild conditions without organic solvent or halogen-containing chemicals. Additionally, kilogram-scale syntheses of super-fine chemicals using hydrogen peroxide in collaboration with commercial laboratories confirmed the individual targeted result for various products.
Titanium dioxide (TiO2) is a promising heterogeneous photocatalyst for decomposition of harmful organic compounds due to its high oxidation activity. Application of TiO2 photocatalysis to selective organic transformations has also been studied. These are, however, unsuccessful because photocatalytic reactions usually lack sufficient selectivity and promote side reactions or subsequent decomposition of formed products. In this review article, we highlighted our recent progress in the development of TiO2 or Ti oxide photocatalysts for selective organic transformations. Our strategies are classified into three categories. The first is the use of micro- or mesoporous TiO2 materials. These pores facilitate the uptake/exclusion of substrates and products and promote selective reaction of substrates while suppressing the reaction of products. The second is the use of monomeric Ti oxide species supported on silica as the photocatalytic active site. They exhibit photocatalytic activity different from bulk oxide materials and promote several reactions selectively. The third is the loading of metal nanoparticles onto the TiO2 surface, which act as a trapping site for conduction band electrons photoformed on TiO2 and as a catalytic active site. These catalysts therefore promote photocatalytic and catalytic reactions simultaneously and facilitate several reactions in one-pot. Heterogeneous photocatalysis that can be operated at mild reaction conditions without the use of harmful chemicals has significant advantages for organic transformations in an economically- and environmentally-friendly way. This review article shows that Ti oxide-based photocatalysts have a potential as a versatile tool in green organic synthesis.
The effects of zeolite structures on alkylation of isobutane with 1-butene were investigated in a batch reactor and in a continuously stirred tank reactor (CSTR) using the proton-form zeolites, H-ZSM-5, H-L, H-Y, and H-*BEA (beta). H-ZSM-5 and H-L zeolite catalysts were deactivated rapidly, whereas H-Y and H-*BEA zeolites retained catalytic activity for a long time in the CSTR, implying that zeolites with three-dimensional large pore systems are useful for preventing deactivation of the catalyst during alkylation of isobutane with 1-butene. H-*BEA synthesized using a dried-gel method (DGC-H-*BEA) showed the most stable activity among the various H-*BEA zeolites. The effects of the synthesis methods and zeolite characteristics were investigated using H-*BEA zeolite. Characterization using NH3-TPD and pyridine-sorption monitored by FT-IR showed that high acid density and high Brønsted acid ratio promoted alkylation of isobutane with 1-butene over H-*BEA zeolite.
DGC-H-beta zeolite catalyst has higher activity and selectivity for the alkylation of isobutane with 1-butene in a CSTR. The cause of the deactivation of the catalyst and the optimum reaction conditions were investigated. Deactivation of the catalyst was caused not by adsorbed carbon species but by hydrocarbons formed by multiple alkylation or oligomerization of olefin. Optimized conditions to avoid these reactions achieved stable selective alkylation.
This article describes the relationship between the different acidic properties of catalytic active sites and their catalytic cracking ability using desulfurized atmospheric residue (DSAR) as a feed. Experiments were carried out in a fixed fluid bed reactor. The acid strength was determined by the temperature of NH3 desorption peak and the number of acid was defined by the amounts of NH3. The catalysts from Y-type zeolites with different unit cell sizes were prepared and evaluated. The lowest number of acid site catalyst shows the lowest conversion and the highest gasoline yield, while the highest one shows the highest conversion and the lowest gasoline yield. Furthermore, the catalysts using wider range of acid site number are evaluated. It was found that the gasoline yield reaches a maximum at a certain number of acid sites for the catalytic cracking of DSAR, but not for that of desulfurized vacuum gas oil (DSVGO). It is important for cracking from DSAR to gasoline to control the number of acid site. Based on these results, an attempt was made to identify the intermediate materials produced during the catalytic cracking of DSAR.
The effect of H2 addition on hydrocarbon oxidation over Al2O3-supported noble metal catalysts was investigated. CO2 was formed below the light off temperature of olefin combustion by the addition of H2 over Pt and Ir catalysts. Particularly for C2H4 combustion, Pt catalysts exhibited significant CO2 formation at 70 °C. CO2 formation at low temperature increased with increasing Pt particle size. CO2 formation in the C2H4 + O2 + H2 reaction at 70 °C over Pt/Al2O3 decreased with increasing contact time. Pt/Al2O3 showed very high activity for hydrogenation of C2H4 even at room temperature. DRIFTS measurement revealed that ethylidene was formed as an intermediate of the C2H4 + H2 reaction, and then consumed by the addition of O2. We conclude that ethylidene intermediates of C2H4 hydrogenation are involved in the low-temperature CO2 formation.
Ready access of hydrocarbon molecules to the catalyst sites is extremely important for petroleum refining catalysts, and access of hydrocarbon molecules to the active sites will result in higher catalytic performance. A new hybrid type of porous material was synthesized by growing MCM-41, a typical mesoporous silica, on both the outer surfaces and within the particles of ultra stable Y (USY) zeolite. Treatment of USY starting material under MCM-41 synthesis conditions was found to transform USY to MCM-41, with the formation MCM-41 on the particle surfaces and between USY zeolite particles. This new hybrid porous structure has improved diffusion of hydrocarbon molecules to the active sites within the USY and MCM-41 pores, resulting in enhanced activity for the hydrocracking of diphenylethane.
Homogeneous charge compression ignition (HCCI) combustion is a complicated phenomenon influenced by both the engine operating conditions and the fuel ignition properties. To achieve a better understanding of the phenomenon, a simplified method applying approximate equations combined with several Arrhenius equations to the Livengood-Wu integral was established for predicting ignition delays in engines, and the calculated results by this method showed good agreement with reported experimental data. Analysis of the behavior of HCCI combustion by this method, including the effects of fuel ignition properties found that the effect of fuel octane number on changing ignition delay is derived from the changing transition temperature from low temperature region to negative coefficient region, and reducing oxygen fraction may have a similar effect on delaying ignition timing. Changing the compression ratio of the engine may be necessary to achieve the correct ignition timing over a wide range of HCCI operation. This simplified method for predicting ignition delay may be effective to analyze the fuel effect on HCCI combustion.