Fischer-Tropsch (F-T) synthesis remains the core technology for producing non-petroleum-based fuels. The product selectivity of F-T synthesis has been restricted by the Anderson-Schulz-Flory (ASF) distribution. New designs of F-T catalysts and reaction pathways that can break these selectivity limitations are extremely important. Notable developments in F-T applications for producing unconventional F-T products such as light olefins (C2-C4), gasoline (C5-C11), jet fuel (C8-C16) and oxygenated organic compounds have been made. Synthesis of these high-value hydrocarbons demands the design of new F-T catalysts that can effectively tune the product distribution beyond the limits of the ASF distribution. Several reaction pathways and high-efficiency F-T catalysts with exceptional catalytic performances have been proposed. This review describes significant advances in terms of rational design of catalysts, particularly for the F-T synthesis of high-demand hydrocarbons. Our perspectives regarding the key factors for enhancing catalytic performances are discussed to open new approaches for future projects.
This review discusses the permeation and separation characteristics, the microstructure and the permeation mechanisms of organosilica membranes with ionic liquid (IL)-like properties, prepared from silylated ILs. The permeation and separation characteristics for binary toluene/H2 mixture, methanol synthesis gas/vapor mixtures, binary toluene/CH4 mixture and binary methanol/CH4 mixture were studied. The membranes showed selective permeation of toluene and methanol against H2, CO2 and CH4 at temperatures over 100 °C. The permselectivities were strongly controlled by the affinity of the permeated molecules for the ILs. The results showed that silylated IL-derived organosilica membranes show potential for selective recovery of organic vapors from inorganic/organic gases. Attenuated total reflectance infrared spectroscopy, N2 adsorption, gas/vapor permeation tests and nanopermporometry were also performed to evaluate the microstructure and permeation mechanisms of the new concept of organosilica membranes. The membrane depended on two permeation pathways, “only the dense IL regions” and “organosilica network-derived micropores + dense IL regions.” Furthermore, the contributions of two permeation pathways to gas permeation were successfully evaluated based on the nanopermporometry characteristics.
In this paper, we introduce our recent research on the precise synthesis of molecular metal oxide nanoclusters, i.e., polyoxometalates (POMs) with precisely engineered active site structures, and their application to organic synthesis reactions. Specifically, using lacunary POMs with coordination sites as molecular templates or multidentate ligands in organic solvents, we established a precise inorganic synthesis method that allowed us to engineer active site structures and unique functions. In organic solvents, the protonation states of lacunary POMs and the dissolved states of metal species can be controlled; thus, we can design functional inorganic materials with the controlled number, arrangement, and oxidation states of metal atoms. Furthermore, using the synergetic effect of POMs with metals or substrates, we pioneered a new methodology of designing POM catalysts to produce catalysts with new reactivity and high performance. On the basis of these methods, visible-light-responsive redox catalysts were developed using intramolecular charge transfers.
The effect of Ce addition to a Bi–Mo complex oxide catalyst supported on SiO2 was examined on the partial oxidation of propylene to acrolein. The catalyst consisted of an oxygen-supply phase in which the lattice oxygen in Mo-oxide was doped with transition metals such as Fe, Ni and Co and was supported by SiO2 and a catalytic-active phase that involved hydrogen abstraction from a reactant in the Bi-center of Bi–Mo oxide, which was supported by the oxygen-supply phase. In the present study, Ce was added to the oxygen-supply phase to enhance its redox nature. Ce addition was advantageous particularly under oxygen-rich conditions in the feed stream. For example, at P(C3H8) = 10.1 kPa and P(O2) = 15.5 kPa at 623 K, the yield of acrolein was slightly enhanced from 57.6 % with 0 % Ce doping to 65.3 % with 20 % Ce doping at 6 h on-stream. However, under more oxygen-rich conditions at P(C3H8) = 10.1 kPa and P(O2) = 31.0 kPa at 623 K, the yield of acrolein was approximately doubled from 27.7 % with 0 % Ce doping to 61.8 % with 20 % Ce doping at 6 h on-stream. Analysis using XPS of the previously used catalysts for the reaction in the absence of gaseous oxygen confirmed the unique redox behavior between the catalytic-active phase and the oxygen-supply phase as the lattice oxygen in the catalytic-active phase was replenished from the oxygen-supply phase to maintain the surface properties of the catalytic-active phase. The XPS results and the remarkable effect of Ce addition to the oxygen-supply phase under oxygen-rich conditions confirmed the validity of the concept of the catalyst preparation consisting of an oxygen-supply phase and a catalytic-active phase.
Although NH3 has been recently regarded as a renewable and/or carbon-free energy source, the use of NH3 fuel is hindered by its high ignition temperature and N2O/NO production. To overcome these problems, catalytic NH3 combustion systems and novel powder (granule) catalysts that showed high activity and low N2O/NO selectivity were previously developed. In this study, we extended our research to investigate the NH3 combustion properties of copper oxides (CuOx)-based honeycomb catalysts (CuOx/Al2O3, CuOx/10Al2O3 · 2B2O3, CuOx/Ag/Al2O3, CuOx/Pt/Al2O3, and so on) for practical applications. Therefore, several monolithic honeycomb catalysts were prepared and their reaction properties were evaluated and compared with those of granular catalysts. The spatial distribution in coated honeycombs before and after thermal aging was examined by the X-ray line analysis technique, which suggested that supported catalysts (thickness of the layers: ca. 100 μm) had homogeneously dispersed CuOx and/or Pt in each catalyst. NH3 combustion properties (activities and selectivities) for honeycomb catalysts were similar to those of the granular catalysts, indicating that their properties were typically independent from the shape of the catalysts. Spectra from X-ray photoelectron spectroscopy were obtained to estimate the fraction of Cu2+/Cu+ for the honeycomb catalysts of CuOx/10Al2O3 · 2B2O3. By density functional theory computations, it was suggested that highly dispersed Ag nanoparticles show a high activity.
Palladium–diimine complexes catalyzed copolymerization of 1-decene with methyl methacrylate (MMA) to produce polymer with vinylene groups in the polymer chain, and a methyl methacrylate group, –CH2–CH(Me)–COOMe, at the polymer end. Previous findings of copolymerization catalyzed by Ni complexes with chelating P–O ligands gave a polymer with an unsaturated end group, –CH = C(Me)COOMe. Other alkyl methacrylates such as n-butyl, t-butyl, and i-amyl methacrylates also copolymerized with 1-decene to yield the end-functionalized polymers. Copolymerization of 1-decene with 2-acetylethyl methacrylate yielded polymer with a terminal ester group, whereas 2-hydroxyethyl methacrylate did not undergo copolymerization. Allyl methacrylate reacted with 1-decene to produce copolymer via preferential insertion of C = C double bond of the allyl groups into the metal-polymer bond. Copolymer of 1-decene and isoprenyl methacrylate contained comonomer units formed via insertion of C = C double bonds of the methacrylic group and of isoprenyl group in 76 : 24 ratio.
The direct alkylation of benzene with n-heptane was investigated using noble-metal-free montmorillonite as a solid acid catalyst. It was found that the catalytic activity of proton-exchanged montmorillonite increased after pretreatments such as heating and ultrasonic irradiation. Aluminum-exchanged montmorillonite was also found to be a good catalyst. Moreover, during the reaction using proton-exchanged montmorillonite, the product selectivity depended on the interlayer distance of the catalyst. Detailed time-course analysis of the selectivity of the alkylation product revealed that, in the case of the catalysts with smaller interlayer distances, the bimolecular reaction occurred preferentially at the surface, resulting in higher selectivity with respect to the target C7 alkylated products (Ph-C7). On the other hand, the monomolecular cracking of heptane in the interlayer spaces resulted in a stable t-butyl cation, yielding t-butylbenzene. Monomolecular cracking also occurred when H-ZSM-5 was used as the catalyst, and the main product was isopropylbenzene.
Jet fuel production from long-chain n-paraffins obtained by hydroprocessing of vegetable oils and animal fats has attracted immense interest. Isomerization and mild cracking are essential to transform long-chain n-paraffins with chain lengths of 16, 18, or 20 into bio-jet fuels consisting of isoparaffins with carbon numbers ranging from 9 to 15. Bifunctional catalysts consisting of noble metal and metal oxide support with solid acid, such as Pt loaded zeolite, are promising for hydroisomerization and cracking reactions. However, the effect of the specific properties of Pt loaded zeolite on the hydroisomerization and simultaneous mild cracking activity are not understood. We investigated the hydroisomerization and cracking of n-paraffins into isoparaffins with shorter chain length by 3-5 carbons over Pt loaded zeolite. n-Decane was first used as a reactant to simplify the reactions, and the effects of zeolite framework structure, solid acid sites, and Pt loading were investigated. 0.5 wt% Pt loaded MFI with Si/Al of 200 was found to maximize the targeted isoparaffin yield. Further modification of the optimized catalyst was performed for isoparaffin production from n-dodecane. Addition of MgO to the catalyst successfully suppressed overcracking and improved the desired isoparaffin yield.
A residue upgrading process system was evaluated which consisted of a solvent de-asphalting (SDA) unit, residue hydrotreating unit (RDS), and residue fluid catalytic cracking unit (RFCC). In the process, de-asphalted oil (DAO) from the SDA is treated in the RDS, followed by conversion in the RFCC. To investigate the effect of the SDA on the RDS performance, detailed analysis of the DAO and atmospheric residue (AR) was conducted using GPC-ICP and FT-ICR-MS. Reactivity of the DAO and AR was also evaluated using an isothermal reactor and an adiabatic reactor. DAO and AR showed similar reactivity in desulfurization, whereas DAO showed higher reactivity in demetallization. Possibly DAO is more active than AR because DAO has a higher number of aromatic rings and lower substituted carbon numbers compared with AR. Temperature increase in the catalyst bed of a commercial RDS unit during DAO processing is different from that during AR processing and the accuracy of temperature prediction using a simulator based on AR processing is not sufficient. However, reaction prediction at the molecular level improved the simulator in both prediction of reactivity and exothermic behavior during the catalytic reaction.
For the application of microwave heating to a continuous gas-flow type reaction using a solid catalyst, a cylindrical cavity system was used for reforming reaction of methane. A single standing microwave was generated within the cavity, resulting in uniform heating of the reaction tube positioned in the center of the cavity. Heating tests were conducted with different loadings of Pd/Al2O3 catalyst. Following hydrogen reduction, 5-10 wt% catalyst loading achieved the best heating effect and avoided reflection of microwaves. Reforming reactions were then conducted over 5 wt% Pd/Al2O3 catalyst using microwave heating and conventional heating, respectively. The conversion efficiency of methane for both steam reforming and dry reforming was higher by microwave heating than by conventional heating. In addition, microwave heating of the Ni/γ-Al2O3 catalyst restricted coke deposition attributed to direct dielectric heating by the microwave irradiation promoting carbon combustion. The results demonstrate the advantages of this microwave heating system for flow-type reactions using a solid catalyst.