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Monolithic catalysts have attracted attention as a substitute for particulate catalyst beds in gas-liquid-solid three-phase reactions. In this work, carbon gel monoliths with a microhoneycomb structure (carbon gel microhoneycombs, CMHs) were synthesized, and Pt particles with an average particle diameter of 3.0 nm were supported on them in a highly dispersed state through the incipient wetness method. In addition, it was confirmed that the supported Pt shows a high resistance to sintering. Hydrogenation of p-nitrophenol was carried out in order to evaluate the catalytic activity of Pt/CMHs in three-phase reactions. As a result, Pt/CMHs showed a high catalytic activity even at ambient temperature and normal pressure. Furthermore, the hydrogenation reaction significantly proceeded even when hydrogen was provided at the minimum flow rate required to complete the reaction. Since Pt/CMHs showed higher reaction activity than the same catalyst in the form of particles, it was concluded that the efficiency of three-phase reactions can be significantly improved by using monolithic catalysts with a microhoneycomb structure.

Microporosity and basic-site density of mixed oxides formed from Mg-Al layered double hydroxides possessing interlayer isethionate (MgAl-Ise) were investigated to seek for a potential application of them to basic catalyst supports for natural gas conversion. The oxide samples were prepared by thermal activation of MgAl-Ise at 500 °C in air, 5% O2 in N2, N2, vacuum, H2 in helium with various concentrations, H2, and NH3 to investigate effects of gas atmosphere. The N2 adsorption data show that Mg-Al mixed oxides obtained by thermal activation of MgAl-Ise in H2, NH3, and N2 possess substantially larger micropore volumes characterized by N2 uptake at the relative pressure

Intercalation of 2-hydroxyethanesulfonate (2-heS) and 3-hydroxy-1-propanesulfonate (3-hpS) into layered Mg–Al double hydroxides (Mg–Al LDHs) allows delamination of layers in water and enables the synthesis of high-surface-area oxides through non-oxidative thermal decomposition. To investigate the roles of anionic heads and hydroxyl tails in these organic sulfonates, 2-hydroxyethanephosphonate (2-heP) and 1,3-propanedisulfonate (1,3-pDS) were tested as analogs of hydroxyalkylsulfonates, and the thermal characteristics of the resultant LDHs were investigated. Exchange of interlayer CO32− with 2-heP proceeds similarly to 2-heS, causing the same degree of interlayer expansion. However, the resultant LDH resists swelling and delamination in water, demonstrating the distinct property enabled by the –SO3− group. Although LDH possessing 1,3-pDS intercalants seems to resist delamination because of the lack of hydroxyl groups, its thermal characteristics resemble those of its 3-hpS counterpart, demonstrating the crucial role of alkyl sulfonate groups to allow the formation of enhanced microporous structures through non-oxidative thermal treatments. Our results show further that even a partial exchange of CO32− by 3-hpS, corresponding to 0.05 equivalents relative to the exchangeable Al sites, triggers unique thermal characteristics observed for LDH-sulfonates.

Analysis of literature data on acid-catalyzed esterification reaction of levulinic acid (LA) with ethanol (EtOH) has suggested that some sulfonated carbon catalysts exhibit higher active-site performance than other solid acid catalysts such as macroreticular resins bearing sulfonic acid groups, zeolites, mesoporous silica functionalized with alkyl- and arene-sulfonic acid groups. To elucidate factors that enable the higher performance of sulfonated carbon catalysts, a series of sulfonated carbon catalysts was synthesized by sulfonating various carbon materials whose concentrations of surface oxygen-containing functional groups, porous structure, and swelling ability differ significantly. The catalysts were tested not only in the liquid-phase esterification reaction of LA with EtOH but also in the reaction of acetic acid (AcA) with EtOH because the latter reaction serves as a test reaction to probe the performance of –SO 3 H sites with minimal influence by mass transfer limitation and to provide an insight into a role of γ-keto group of LA in catalysis. The results show that all catalysts exhibit nearly the same turnover frequency per –SO 3 H site in the esterification reaction of AcA with EtOH despite widely different structural properties. In contrast, the data indicate that neighboring functional groups such as –COOH and –OH facilitate the reaction of LA with EtOH presumably through hydrogen-bonding interaction between these surface functional groups and γ-keto group of LA. These results suggest a general design strategy to improve the performance of solid acid catalysts further by precisely tuning the distance between –SO 3 H sites and neighboring functional groups.

Ternary Mo–V oxide nanocrystals (Nano-MoVO) were hydrothermally synthesized in the confined space of a mesoporous carbon template and tested in the oxidative dehydrogenation (ODH) of ethane and propane. The synthesized nanocrystals are approximately 60 nm in length, 20 nm in diameter on average, and possess a structure resembling orthorhombic MoVO (Orth-MoVO) as indicated by spectroscopic and microscopy characterization. The Nano-MoVO catalyst has a 5-fold higher mesopore volume and a 4-fold larger external surface area than an Orth-MoVO synthesized by a conventional method (Orth-MoVO) as characterized through N2 adsorption analysis. Nano-MoVO shows similar activation energy in the ODH of ethane compared with other conventional MoVO catalysts. However, Nano-MoVO exhibits significantly higher propane/ethane activation rate ratio and higher propene selectivity even in the absence of elements such as Te and Nb that suppress overoxidation of propane-derived species to COx. The results suggest the benefits of the nanocrystalline morphology to limit overoxidation.

For the preparation of physically-activated carbons with ultra-high surface areas that are comparable to those of chemically-activated carbons, we synthesized meso-, macroporous carbons from phenolic resins using poly(methylmethacrylate) particles as a template and activated them using CO2. Our aim was to achieve uniform activation by reducing the practical depth within the carbon which needs to be activated. Our results show that the shorter the practical depth becomes, the higher the achievable BET surface area becomes. Extremely high BET surface areas (~3000 m2 g−1) can be attained by reducing this depth to the order of a few tens of nanometers. We also relate the practical length of the developed nanopores with the practical depth through the results obtained from EDLC measurements. The results reveal that the shortening of the practical activation depth also leads to the shortening of the lengths of the nanopores introduced during activation.

Carbon microhoneycombs (CMHs), which can be prepared from a resorcinol formaldehyde (RF) hydrogel using ice crystals as a template, are attractive materials for industrial applications such as solid catalysts and adsorbents in flow system reactors. For such applications, pores in a material are important for mass transfer, but the mesopore volumes of CMHs are smaller than that of typical RF-derived carbons because ice crystals compress RF gels during freezing, and mesopores partly collapse. The introduction of mesopores into CMHs requires an additional step such as HCl treatment in the preparation process, and this increases the preparation time. In this work, we developed a convenient method for introducing mesopores into CMHs, in which dextran was added to the initial RF solution. This simple step increased the mesopore volume from 0.015 to 0.191 cm(3)/g. We investigated the porous structure of the sample at each step in the preparation, and found that dextran protected the porous structure of the RF hydrogel from growth of ice crystals, enabling mesopore introduction. A combination of dextran addition and HCl treatment further increased the mesopore volume to 0.753 cm3/g; this cannot be achieved using HCl treatment alone. This may be because the HCl solution can diffuse through the mesopores introduced by dextran addition, and this promotes pore formation. (C) 2016 Elsevier Inc. All rights reserved.

To investigate the effects of the porous structure of carbon support for bimetallic PtRu PEFC anode catalysts on their CO tolerance, a series of Resorcinol-formaldehyde carbon gels with different resorcinol to catalyst (R/C) ratios (i.e., 200, 800 and 1000) were synthesized and used to support Pt2Ru3 nanoparticles. Synthesized catalysts were characterized by powder X-ray diffraction, N2 gas adsorption/desorption experiments, and scanning transmission electron microscopy. CO tolerances were evaluated by using a single cell in a H2 feed in the presence of CO ranging from 100 to 2000 ppm. The potential difference of the cell using Pt2Ru3/RC1000ac58 anode catalyst was 0.655 V whereas the cell using a commercial Pt2Ru3/C catalyst showed a voltage of 0.570 V in the presence of 500 ppm CO. The results reveal that high modal size and volume of mesopore enhance diffusivity of CO resulted in effectively oxidization of CO.

Pt–Ru/SnO2/C catalysts were prepared by a rapid quenching method. The structure and morphology of Pt–Ru particles in Pt–Ru/SnO2/C are controlled to obtain the same Pt–Ru particle as that in a commercial Pt–Ru catalyst. The Pt–Ru/SnO2/C and commercial Pt–Ru catalysts were characterized by X-ray diffraction and scanning transmission electron microscopy. Electrochemical activities were evaluated by CO stripping voltammetry, single cell tests, in situ infrared reflection–absorption spectroscopy (IRRAS) and surface-enhanced infrared absorption spectroscopy (SEIRAS). The Pt–Ru/SnO2/C catalyst showed the same structure, morphology and catalytic activity for hydrogen oxidation reaction (HOR) in the absence of CO as those of a Pt–Ru/C catalyst. Both the activity for electrochemical CO oxidation and Pt–CO bond strength were quantitatively evaluated. The addition of SnO2 decreased the Pt–CO bond strength with maintained HOR activity to enhance CO tolerance.

Flexible film-type catalysts were synthesized by encapsulating urease within a κ-carrageenan gel network supported on a cellulose-acetate membrane filter. Synthesized film-type catalysts are flexible and can be easily formed into a shape that is suitable for a specific process configuration. The filter membrane has macropores about 200 nm, which are formed by interconnected bead-shaped membrane material. Scanning electron microscopy shows that the surface of the membrane material is coated homogeneously with the κ-carrageenan hydrogel. Urease entrapped within the gel network hardly leaches out during urea hydrolysis catalysis conducted at 310 K in a batch reactor and exhibits high catalytic performance. Analysis of the reaction data by the Michaelis–Menten equation shows that the film-type catalyst shows kinetic parameters ( K M and V max ) and apparent activation energy (24 kJ mol − 1 ), which are all similar to those found for free urease. Estimation of the mass transfer rate of urea within the κ-carrageenan network and the urea hydrolysis rate show that the diffusion rate of urea within the thin film is five orders of magnitude higher than the reaction rate. The film catalyst can be recycled at least 7 times with

A series of sulfonic-acid-containing carbon catalysts were synthesized through the pyrolyzation of resorcinol–formaldehyde resins and subsequent sulfonation to investigate the tunability of their pore structure and surface properties. These catalysts were characterized by nitrogen gas adsorption, water vapor adsorption, elemental analysis, Boehm titration, and IR spectroscopy. Catalytic consequences of these properties were examined using two esterification reactions in which reactants of substantially different sizes (oleic acid vs acetic acid) are involved as well as the condensation of furfural with 2-methylfuran. The esterification of acetic acid with ethanol proceeded at nearly the same activity (TOF ∼ 0.02 s–1) for all synthesized catalysts regardless of the variation of their surface and pore properties. Poisoning experiments of acid groups in the synthesized catalysts with NaCl indicate that nearly all −SO3H groups are accessible to the reactants. However, the esterification of oleic acid with met...

Efficacy of a new approach for the synthesis of graphene oxide (GO) nanosheets that has been recently reported (Ogino et al. in Chem Mater 26:3334–3339, 2014) was investigated further using graphite oxides with various degrees of oxidation and average particle sizes. The approach consists of rapid freeze–thaw cycles of water containing graphite oxide, which enables the efficient exfoliation of graphite oxide layers with the minimal fragmentation of GO sheets. The method is effective for the exfoliation of graphite oxides with C/O atomic ratios ≤2.6 as shown by experiments with various degrees of oxidation of graphite oxides. When this method was tested for large particle-size graphite oxide that had been prepared from graphite with the average particle size of 60 μm, it formed approximately tenfold larger GO sheets than those prepared using sonication. Exfoliation experiments conducted at different freezing rates of water demonstrate that a faster freezing rate of water yielded a higher concentration of a dispersed GO solution. Thus, the results support the hypothesis that rapid phase change enables efficient layer exfoliation.

Resorcinol–formaldehyde carbon gels (RFCs) show several advantageous properties as a catalyst support over other carbons, as their pore volume and pore size can be readily tailored, for example, via CO2 activation. In this study, RFCs were synthesized with various activation degrees (burn-off) as 0, 37, 58, and 88% and used as the support for a PtRu anode electrode; a commercial Pt2Ru3/C anode catalyst was used as a reference. The catalysts were characterized by powder X-ray diffraction (PXRD), BET surface area, transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). The performance and CO tolerance of the obtained catalysts were tested through single cell performance analysis with CO contaminations ranging from 100 to 2000 ppm. The prepared Pt2Ru3/RFC catalysts showed superior CO tolerance. Especially Pt2Ru3/RFC prepared using an RFC with a burn-off of 58% (RC1000Ac58) showed the highest performance and best CO tolerance. The activation degree could affect the volume...

A carbon-based monolithic acid catalyst with a honeycomb structure (CMHC) was synthesized via carbonization of a resorcinol-formaldehyde resin and subsequent sulfonation using sulfuric acid. The CMHC has nearly straight flow-through macropores (e.g., 47–78 μm) formed by the directional freezing of the resin precursor. These macropores are surrounded by thin carbon walls of approximately 6-μm thickness that are micro- and mesoporous as characterized by nitrogen adsorption experiments. The straight macropores enable a low hydraulic resistance to a liquid flow as demonstrated by >1000-fold less pressure drops of water flowing through the CMHC than those calculated for a packed bed of spherical particles with the same diameter as the approximate wall thickness of the CMHC. The CMHC shows a stable catalytic activity in the liquid-phase esterification of acetic acid with ethanol at 333 K in a flow reaction system for 50 h of operation. These results show prospective features of the CMHC for applications in flow...

A honeycomb-type silica monolith was functionalized with sulfonic acid groups to synthesize a solid acid catalyst for flow reaction systems. The sulfonic acid groups were introduced via anchoring of 3-mercaptopropyltrimethoxysilane (MPTS) on the silica surface and subsequent oxidation using a H2O2 solution. The honeycomb-type monolith used as the substrate was prepared using ice crystals as a template and was found to have a high open frontal area of ≈85% and flow-through macropores (≈27 μm in diameter) that are surrounded by silica walls (≈2 μm in thickness). The catalyst was tested by the liquid phase esterification of ethanol with acetic acid at 333 K in a batch reactor as well as a flow reactor. The catalyst was found to exhibit about 2-fold higher catalytic activity than Amberlyst-15 in a batch reactor. The catalyst also showed a stable catalytic activity for 24 h in a flow reactor.

In this work, the growth behavior of carbon nanofibers synthesized using the liquid pulse injection technique was clarified by analyzing samples collected at different growth stages. It was confirmed that, due to the high catalytic activity of the ultrafine metal catalyst particles generated through this technique, the fibers elongate at an extremely high rate during the initial stage of growth, which leads to the high efficiency of carbon nanofiber production. Owing to this high elongation rate, the elongation process and thickening process can be practically considered as two consecutive processes. This allows the modification of the production sequence, resulting in a significant enhancement in production efficiency.

In this work, the synthesis of a strong acid ion-exchange resin with a monolithic microhoneycomb structure was attempted using the ice templating method, a new micromolding technique developed by the authors. The obtained monoliths were found to have micrometer-sized straight channels, and the thickness of the walls which form the channels were also in the micrometer range. Through titration experiments, it was confirmed that the monoliths have a sufficient ion exchange capacity and strong acidity. The monoliths also showed catalysis in esterification reactions which indicates that they can be used as an effective solid acid catalyst with an extremely low hydraulic resistance in various commercial reactions.

Selective de-activation of acid sites located near the outer surface of zeolite was examined using the catalytic cracking of silane (CCS) method. From FT-IR analysis, adsorption species of silane compounds on the acid sites of zeolite during calcination were investigated. Moreover, the effects of types of silane compounds on the changes in zeolite properties, including the amounts of adsorbed ammonia and benzene within zeolite, prior to and after CCS treatment, were examined. The CCS method using diphenylmethylsilane (DPM-silane) was effective in de-activating the acid sites located near the outer surface of ZSM-5 zeolite. Olefin synthesis from acetone was carried out using ZSM-5 zeolite catalysts. The ZSM-5 zeolite after the CCS treatment using DPMsilane exhibited high olefin selectivity as well as low aromatic selectivity.

Wattle tannin–furfural (TFu) gels are synthesized by the sol–gel polycondensation of wattle tannin with furfural by using sodium hydroxide as a catalyst and cured at 363 K. After cured, the TFu hydrogels are treated in hydrochloric acid (HCl) solutions with various variables as follows: aging temperature, HCl concentration and pH. TFu cryogels aged are then freeze-dried and pyrolyzed under an inert atmosphere to obtain TFu carbon cryogels. The TFu and carbon cryogels were characterized by N 2 adsorption and scanning electron microscope. The high HCl concentration yields the increase of mesopore volume almost twice especially at high temperature and the mesopore size distribution can be greatly developed sharper and narrower when the high concentration of HCl or/and the high temperature are used. Moreover, this method is the versatile approach for developing the mesopore structure of the low and high porous TFu hydrogels and has no serious problem of weight loss after treatment.

Wattle tannin–furfural (TFu) carbon cryogels are synthesized by sol–gel polycondensation of wattle tannin with furfural by using sodium hydroxide (NaOH) as a catalyst, dried by freeze-drying technique and then pyrolyzed under inert atmosphere, respectively. The amounts of wattle tannin (T), furfural (Fu), NaOH (C) and distilled water (W) are changed for preparing the mesoporous TFu carbon cryogels. The mole ratio of tannin to catalyst T/C plays a crucial role for the synthesis of TFu organic and carbon cryogels. The results suggest that the T/C ratio should be above 0.25 but

Wattle tannin-furfural (TFu) hydrogels were synthesized by the sol–gel polycondensation of wattle tannin with furfural by using three types of base catalysts (NaOH, Na2CO3 and NaHCO3). TFu cryogels were prepared by freeze drying of the hydrogels and TFu carbon cryogels were obtained by pyrolysis of the cryogels in an inert atmosphere. The TFu and carbon cryogels were characterized by N2 adsorption and scanning electron microscope (SEM). The effect of catalysts on porous properties of carbon cryogels resulted in different ways: (1) NaOH enhances increasing mesopore volumes and surface area of carbon cryogels and (2) Na2CO3 and NaHCO3 cause decreasing those of carbon cryogels. The TFu and carbon cryogels prepared by using NaOH as a catalyst possessed large mesopore volumes comparing with micropore volumes. Even though the TFu cryogels have surface area and mesopore volumes smaller than the resorcinol-formaldehyde (RF) cryogels, the carbon cryogels have unique porous properties differed from the RF carbon gels. The properties are summarized as follows: (1) the mesopore volume changes insignificantly after pyrolysis, (2) the pore radius is increased after pyrolysis and (3) micropores are not greatly developed during pyrolysis.

Recently we introduced the “ice templating” method, a new method which allows the synthesis of nanoporous materials with unique morphology, such as microfibers and microhoneycombs. In this method, materials are synthesized by freezing their parent hydrosols or hydrogels unidirectionally. Ice crystals which grow within the precursor during freezing act as the template. Therefore, the template can be easily removed through simple thawing and drying, which is a unique and beneficial feature of this method. This paper will first describe the outline of this new method and next, the details about methods to control the dimensions of the materials obtained through it. Comments about the range of applicability of this method will also be provided.

We propose a new TPD method for simultaneously characterizing the acidic and basic properties of solid catalysts by utilizing the co-adsorption of NH 3 and CO 2 on catalysts. First CO 2 was adsorbed on the catalyst sample; then NH 3 was adsorbed on it. Another adsorption sequence of NH 3 and CO 2 , and CO 2 and NH 3 single adsorptions were also conducted. The TPD measurements were carried out by heating the catalyst sample from 373 to 773 K at a heating rate of 2.5 K min −1 in a helium stream under a total pressure of 1.3 kPa. In solid acid catalysts, there is little difference in the NH 3 -TPD spectra between single and co-adsorption systems. This results from the absence of any induction effect between the acid and base sites, because the number of base sites in the solid acid catalyst is very small. In contrast, in a solid acid–base catalyst of alumina, a remarkable difference in the NH 3 -TPD spectra was observed between single adsorption and co-adsorption systems. The difference in the TPD spectra between single and co-adsorption systems was ascribed to a strong induction effect appearing on the acid and base sites, which was proved by an in situ IR measurement. The validity of the TPD method was examined by correlating the number of the strong acid sites to catalytic activities of dehydrolysis of ethanol over solid acid and solid acid–base catalysts. In solid acid–base catalysts, the number of strong acid sites was calculated from the activation energy distribution for the desorption of NH 3 in a co-adsorption system because of the strong induction effect. A proportional relationship between the intrinsic reaction rate constant, which is based on the concentration of ethanol within the catalyst, and the number of strong acid sites could be obtained, regardless of the catalysts or their types or pore structure.

Mesoporous carbon gels are usually obtained by pyrolyzing resorcinol–formaldehyde (RF) gels, which are synthesized via the sol–gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution followed by drying. However, mesoporous carbon gels cannot be prepared under the conditions of high catalyst concentration or high pH of RF solution even by using supercritical drying or freeze drying. In this work, mesoporosity of carbon cryogels is improved by ultrasonic irradiation to RF solution. It is found that the gelation time of RF solution becomes greatly short by ultrasonic irradiation and that ultrasonic can improve mesoporosity of carbon cryogels prepared at high catalyst concentration (C/W). Although the carbon cryogels prepared from C/W = 80 mol/m3 have no mesopores, the carbon sonogels prepared by ultrasonic irradiation under the same catalyst condition have sharp mesopore size distribution. The utilization of ultrasonic in the preparation of RF gel is an interesting way in improving mesoporosity of carbon gels prepared at high C/W or pH.

Keggin-type heteropoly acids (HPAs) were immobilized in the unique network structure of resorcinol-formaldehyde (RF)-derived carbon gels. Two methods were employed for immobilization, one by impregnating 12-tungstophosphoric acid (PW12) in a wet RF hydrogel followed by drying and carbonization of the support, and the other by synthesizing 12-molybdophosphoric acid in a slurry mixture of carbon gel particles and deionized water. It was found that significant amounts of the acids could be immobilized to carbon gel supports by both methods, and large amounts of the acids remained in the carbon supports even after long-term hot water extraction. Moreover, the obtained complexes were found to show catalysis in the synthesis of methyl-tert-butyl ether from methyl alcohol and tert-butyl alcohol, indicating that they could be practically used as solid acid catalysts in various reactions which involve water.

In this work, efforts were made to improve the preparation method of “ship-in-the-bottle” type 12-molybdophosphoric acid (PMo12) encaged Y-type zeolite catalysts. First, the possibilities of modifying other popular heteropoly acid synthesis methods to prepare encaged catalysts were examined. It was found that only the conventional method, which uses MoO 3 and H 3 PO 4 for PMo12 synthesis, led to a significant amount of PMo12 encaging. Next, using this conventional method, the influences of temperature and solvent addition during synthesis on the amount of PMo12 encaging and the stability of the resulting encaged catalyst were investigated. It was found that by adjusting the reaction temperature, the stability of the resulting encaged catalyst could be enhanced to higher levels. Moreover, it was found that by adding t -butyl alcohol (TBA) to the solution used for catalyst synthesis, an active and stable encaged catalyst can be prepared even at low synthesis temperatures.

A ZSM-5 zeolite catalyst membrane without pinholes was successfully prepared by synthesizing ZSM-5 zeolite layer on the outer surface of a cylindrical alumina ceramic filter. In the preparation of the membrane, to enhance the smoothness of the outer surface of the filter, a filter with pores of 0.1 μm in diameter was employed. Furthermore, the hydrothermal synthesis was repeated using the same samples. The obtained zeolite membrane showed a molecular sieving effect for the permeation of gaseous xylene and diethylbenzene isomers. The ratio of the permeability of the para-isomer to the meta-isomer was about 2.7 for xylene and 6.0 for diethylbenzene, respectively. The membrane was used as a catalytic membrane reactor to recover olefins from methanol. By adjusting the diffusion rate to the chemical reaction rate for producing olefins within the ZSM-5 zeolite layer, olefins were successfully produced at a high selectivity (about 80-90%) from methanol at high conversions of 60-98%.

Intracrystalline and effective diffusivities of ethane, propane, ethylene and propylene were measured for several kinds of MFI-type zeolite, such as silicalite-1, H-MFI, Cu- and Co-MFI-type zeolites at temperatures ranging from 323 to 823 K . The intracrystalline diffusivity represents the mobility of molecules within zeolite crystals, and was found to be reduced to 1/100 for paraffins and 1/1000 for olefins by the existence of active sites (proton, Cu and Co ions), as compared with silicalite-1. The effective diffusivity was evaluated by multiplying the intracrystalline diffusivity by a partition factor. Although the intracrystalline diffusivity of olefins was about 1/10 to 1/100 of that of paraffins, the effective diffusivity of olefins was almost equal to that of paraffins. The calculated effective diffusivity of ethylene within Cu-MFI was in good agreement with those evaluated by the kinetic analysis of the catalytic decomposition of NO with ethylene over Cu-MFI catalyst.

The possibility of recovering useful hydrocarbons from oil palm waste derived lignocellulose (palm shell oil) using steam tolerant catalysts was investigated. The examined catalysts were rare earth metal exchanged Y-type (REY) zeolites, nickel supporting REY zeolites and FeOOH catalysts. It was found that palm shell oil could be converted to a mixture which mainly contains phenol, acetone and butanone without hardly generating solid residues when a FeOOH catalyst was used. Therefore, by catalytic reaction, this waste-derived material may become a new and abundant chemical source. The catalytic activity of this FeOOH catalyst can be enhanced by supporting ZrO 2 on it. It was found that oxygen transfer during reaction occurs mainly from H 2 O to the products, not from the oxygen of the catalyst. It is assumed that the supported ZrO 2 plays a role of the decomposition of H 2 O adsorbed on the catalyst, yielding active hydrogen and oxygen species, which is also supported by the results of thermal desorption spectra and Mossbauer spectroscopy analysis of the catalyst.

The stability of a "ship in the bottle" type 12-molybdophosphoric acid encaged catalyst was drastically enhanced by stabilizing the acidic species of the catalyst by partial exchange of its protons with cesium cations. This catalyst practically acted as a solid catalyst in the esterification of acetic acid with ethanol.

Nickel and rate earth metal exchanged Y-type zeolite catalyst (Ni-REY) was prepared for producing light fuels (gasoline and kerosene) by the catalytic cracking of heavy oil from waste plastics in a steam atmosphere. The Ni in the catalyst was found to exhibit catalysis for transportation of hydrogen atoms from steam to hydrocarbons. In a steam atmosphere, strong acid sites of the catalyst, which usually cause excessive cracking, were covered with steam molecules, leading to a high yield of liquid fuels. Experiments using MFI zeolite in a nitrogen atmosphere were also conducted for comparison. During the repetition of sequences of reaction and regeneration of the catalysts, MFI zeolite was gradually deactivated, whereas Ni-REY was found to show constant activity. Furthermore, the selectivity towards gasoline was higher than MFI zeolite (Ni-REY in steam: 78%, MFI type zeolite in N2: 35%).

Changes in the acidic properties and catalytic activity of MFI-type zeolite catalysts caused by dealumination in a steam atmosphere were examined. The reaction rate constant of the cracking of n -hexane was used as an index of the catalytic activity. The zeolite catalysts were exposed to a steam atmosphere for 3–20 h under a steam partial pressure of 1.0–101 kPa, and a temperature of 773 K. The amounts of acid sites induced by each kind of aluminum atoms inside and on the outer surface of the steamed zeolite crystals were measured separately by TPD methods with ammonia and 2,6-diethylaniline. Dealumination in a steam atmosphere was found to proceed as follows: first, tetrahedral aluminum atoms are extracted out of the framework and transformed into partially distorted octahedral aluminum atoms, which also induce acid sites. These atoms move to the outer surface of the zeolite crystals. During this movement, a part of them is pushed out of the crystals and turn into perfectly octahedral ones, which never induce acid sites. The remaining partially distorted octahedral aluminum atoms arrive at the outer surface of the crystals, and then they are pushed out of the crystals and turn into perfectly octahedrally coordinated aluminum atoms. With the progress of the dealumination, the catalytic activity increased at the beginning of the process, reached a maximum value, and then decreased. This phenomenon was considered to be dependent on the change in the amount of partially distorted octahedral aluminum atoms on the outer surface of the zeolite crystals.

In the production of vapor-grown carbon fibers, ultrafine iron catalyst particles play an important role in the elongation process of the fibers. The activity of the catalyst particles depends strongly on their sizes. Therefore, in this work, ultrafine iron catalyst particles were produced under various reaction conditions using the liquid pulse injection technique, and were collected to investigate the influence of the reaction conditions on the size distribution of the obtained particles. The varied conditions were, the concentration and amount of ferrocene, which was used as the source of the catalyst material, and the velocity of the carrier gas at a fixed temperature. Each of them had a significant influence on the size distribution. From the obtained distribution curves, the relationship between the amount of catalyst particles having diameters in the range 20–30 nm, and the yield of fibers produced under the same set of reaction conditions was investigated. It was found that the yield increases with the increase in the number of catalyst particles in the size range from 20 to 30 nm. Furthermore, a model was developed to predict the size distribution of particles produced under various reaction conditions. This model was found to well represent the experimental data.

12-molybdophosphoric acid encaged in the supercages of Y-type zeolite was synthesized from molybdenum oxide and phosphoric acid, in a slurry mixture of Y-type zeolite crystals and deionized water. After thorough washing in hot water, the 12-molybdophosphoric acid was found to remain in the Y-type zeolite, at an amount estimated to be 0.09 g (g-support)−1. Catalysts thus obtained were found to show activity for the esterification of acetic acid with ethanol, indicating that this catalyst could be used as a solid acid catalyst in various liquid phase reactions which involve water.

A method, called the ac -TPD method, was presented for calculating the density distribution function of the adsorption enthalpy of ammonia by utilizing the temperature-programmed desorption (TPD) spectrum of ammonia from solid catalysts measured under complete adsorption equilibrium conditions. TPD spectra were measured using a gas stream containing ammonia, at a relatively large concentration compared to the amount of ammonia desorbed from the catalyst. Under these conditions, the concentrations of ammonia both inside the catalyst particles and in the gas phase are kept almost constant during the experiment. This situation meant that the amount of ammonia remaining on the catalyst was at an equilibrium state and dependent on the temperature and concentration of ammonia. Therefore, it could be assumed that the adsorption equilibrium of ammonia on acid sites can be expressed by a Langmuir-Hinshelwood type equation, which has an adsorption enthalpy and a pre-exponential adsorption equilibrium constant corresponding to the strength of an acid site. The overall TPD spectrum is represented by the sum of the spectra from acid sites with different acid strengths. Under these assumptions, the desorption temperature was related to the adsorption enthalpy of ammonia, and a relationship was derived between the overall TPD spectrum and the density distribution function of the adsorption enthalpy. The distribution function obtained by this method can be used for evaluating acidic properties of solid catalysts. The heat flux required for the desorption of ammonia from acid sites during the TPD experiment was calculated using the obtained distribution. The value was found to agree well with that directly measured by a differential scanning calorimetric apparatus. The density distribution of the adsorption enthalpy ( Q ) was compared to the distribution of activation energy for desorption of ammonia ( E ) by a method, called dc -TPD, which was reported previously by us. This comparison gave the relationship between Q and E , and it was found that the Q value was smaller than the E value by about 15 kJ mol −1 .

Three series of experiments were conducted to collect information for the design of a commercial scale reactor for the production of low cost vapor grown carbon fibers (VGCFs). Firstly, the effects of reaction conditions on the yield of vapor grown carbon fibers were investigated using the newly developed liquid pulse injection technique. The examined conditions were the flow rate of the carrier gas, and the amount of the catalyst source injected into the reactor as a liquid pulse. Yields up to 40% were attained under optimized conditions. Secondly, VGCFs were continuously produced by intermittently injecting the catalyst source into the reactor (intermittent liquid pulse injection technique), and the effect of the intervals of the injections on the amount of VGCFs obtained was also investigated. VGCFs were successfully obtained using this method. Finally, the growth sequences of VGCFs were investigated using benzene, toluene and xylene as the carbon source. VGCFs were obtained from each carbon s...

Long vapor grown carbon fibers (VGCFs) have been obtained using a new method, the liquid pulse injection (LPI) technique. A benzene solution of ferrocene was injected to the surface of the hot wall of the reactor. Ferrocene was rapidly heated and decomposed, yielding ultra-fine iron catalyst particles, on which VGCFs were grown. VGCFs as long as 44 mm were obtained within 30 seconds using this new technique. Furthermore, the maximum average growth rate of them was over 2500 μm/s, which is much higher than those of conventional VGCFs. This growth rate permits the production of VGCFs longer than 10 mm within a few seconds.

Structure formation during the sol-gel transition of resorcinol-formaldehyde (RF) solutions was traced by dynamic light scattering (DLS) and static light scattering (SLS) techniques. The decay time spectra obtained by DLS revealed that both the growth rates of colloidal particles formed during the early stage of the sol-gel transition and the time required for the colloidal particles to form a firm network structure could be related to the ratio of catalyst to water (C/W) of the starting RF solution. SLS results indicated that the molecular weight of colloidal particles increased with the progress of the sol-gel transition, the rate of which was also affected by the value of C/W. The mesoporosity of RF aerogels, which were prepared by drying RF hydrogels with supercritical carbon dioxide, was confirmed to depend on the size of colloidal particles estimated from the decay time spectrum collected at the last stage of the sol-gel transition.

Carbon gels are unique porous carbons, which are typically obtained through the carbonization of resorcinol–formaldehyde gels. They are practically an aggregate of nanometer-sized carbon particles. Nanopores, mostly in the size range of mesopores, exist between the particles. Smaller pores, micropores being the majority, also exist within the particles. Therefore, this material has a hierarchical pore system in which short micropores are directly connected to mesopores. This pore system can be tuned quite precisely, by simply adjusting the synthesis conditions, such as the amount of catalyst used for synthesis, and the drying conditions of the precursor RF gel. As the precursor RF gel is synthesized through a sol–gel transition, there is a high possibility that its morphology can be easily controlled. We have examined the possibility of controlling of the morphology of carbon gels, and have succeeded in obtaining them in the form of disks, microspheres and microhoneycombs. Details of such carbon gels are reported. [TANSO 2012 (No. 255), 266–273.]