A series of Cr–V mixed oxide catalysts (CrVO4, Cr1−xAlxVO4 and CrV1−xPxO4) have been prepared by "soft chemistry" technique. By mixing the aqueous solution of the raw materials and controlling the pH value, chromium vanadates (CrVO4-I and III) were prepared as the pure orthovanadate crystalline form. Prepared chromium vanadates were employed in the vapor phase oxidation of 2-, 3-, and 4-picolines in order to investigate the relationship between the catalysis and structure of chromium vanadate. CrVO4-I (monoclinic) showed much higher activity than CrVO4-III (orthorhombic), suggesting that the bridging oxygen in the V–O–Cr bond is responsible for the catalytic activity. When a part of Cr or V was replaced with Al or P without changing the CrVO4-I type structure, the activities were enhanced. The acidity increased by the replacement of Cr with Al and V with P in CrVO4-I, resulting in the accelerating desorption of products. A partial replacement of V with P significantly improved activity and this is probably due to the modification of the redox properties of V–O–Cr site in addition to the accelerating desorption of products. An addition of large amount of steam in the reactants improved the yield of desired products. Both Lewis and Brønsted acid sites were detected on the surface of CrV0.95P0.05O4, and the number of the latter increased by the addition of steam. The enhanced activity by the addition of steam is interpreted by the fact that Brønsted acid sites are produced by the hydrolysis of V–O–Cr bond on the surface and activate picoline molecules by withdrawing the electrons of the pyridine ring, and at the same time, enable to accelerate the desorption of the acid products. Even in the absence of gaseous oxygen, the oxygenated products were formed, thus, a Mars and van Krevelen mechanism was suggested.
Direct fuel cells using a liquid fuel are ideal power sources for use in mobile electronics and transportation. Research and development on direct fuel cells (direct-fueled fuel cells) using a polymer electrolyte membrane were carried out. Biomass fuels, including L-ascorbic acid, ethanol and D-glucose, were studied as fuels. A direct L-ascorbic acid fuel cell could be operated even without an anode catalyst. The maximum power density of direct ethanol and glucose fuel cells was significantly increased by the use of an anion-exchange membrane. Hydrazine and borohydride were studied as carbon-free fuels. An anion-exchange membrane was needed in the direct hydrazine PEM fuel cell to suppress the crossover of hydrazinium cation. A rhodium porphyrin molecular catalyst was developed as an anode catalyst for use in direct borohydride fuel cells. Rhodium porphyrin catalysts suppress the generation of hydrogen due to the hydrolysis of borohydride much more than a platinum catalyst.
The resistance to coking and metal deposition from heavier crude feedstocks is important to a fluid catalytic cracking (FCC) catalyst. The catalytic cracking of n-hexadecane (n-C16H34) as a model compound was studied on the ultrastable Y zeolite (USY) catalysts with nanoporous (np, 5-50 nm pore diameter) Al2O3. A combination of two np Al2O3 types with well controlled pore size (7 nm or 35 nm) was employed as binder and matrix. The catalyst made with the matrix from the combination of the two pore sizes, with an average pore size of around 14 nm, exhibited higher cracking activity and lower rate of degradation by coking, similar to the catalyst with the single matrix pore size of 14 nm. A USY zeolite catalyst fabricated with only the small pore size np Al2O3 exhibited better resistance to hydrothermal regeneration under model conditions than a catalyst with the large pore size np Al2O3. A catalyst partly containing small pore size np Al2O3 exhibited better resistance to hydrothermal regeneration after intentional deposition of vanadium than a catalyst made of the small pore size np SiO2. Therefore, the small pore size np Al2O3 has functions to protect the zeolite component and its activity, against both of high temperature steam and vanadium species, by binding on the zeolite surface and trapping the vanadium which easily moves over np SiO2 during regeneration. Furthermore, it was clarified that the large pore size np Al2O3 in the mixed matrix can also act as a trapping site for Ni deposition to reduce coking with hydrogen generation on the deposited Ni and protection of the zeolite component activity.
The influence of iron compounds accumulation on FCC catalyst has been reported in viewpoint of drop of apparent bulk density and deterioration of cracking activity. In this paper, these iron issues were investigated by using equilibrium catalyst. Accumulation of iron compounds on catalyst led to nodule formation to decrease ABD of equilibrium catalyst. However, in some cases, lowering of ABD was observed even in little nodule formation. The magnetic susceptibility of the catalysts increased with iron oxide content. This suggests the lowering of ABD is mainly due to magnetic repulsion between catalyst particles. From selected area electron diffraction analysis, iron compounds were found to be composed of Fe3O4, Fe2O3 and NiFe2O4, and then magnetism of the catalyst might come from formation of Fe3O4. Peeling of the iron compounds deposited on the surface of catalyst particles resulted in recovering the FCC performance of equilibrium catalyst. From these results, it was suggested that iron compounds deposited on mainly catalyst surface plugged pores to disturb diffusion of feed oil and led to lower FCC performance.
Glycerol pretreatment of bio-oil has been found to be effective for producing rapid ethanolysis, which is of great usefulness in biodiesel production for sub-Saharan regions such as Malawi. However, the reaction characteristics of glycerolysis have not been elucidated, so design of a novel biodiesel production process has been hindered. In this study, the overall thermodynamic reaction properties were evaluated and the reaction kinetics were determined. Pre-mixtures of groundnut (Arachis hypogaea) oil feedstock, glycerol (GL), and calcium hydroxide (Ca(OH)2) were prepared in a 300-mL flat-base round flask reactor and heated at different temperatures and for different times. The results showed that thermal pretreatment at 180°C for 5 h significantly enhanced triglyceride (TG) decomposition and initial diglyceride (DG) and monoglyceride (MG) concentrations as reactive intermediates for ethanolysis. The change in enthalpy, entropy and Gibbs free energy were determined, which led to the determination of the reaction equilibrium. First-order kinetics for glycerolysis of TG and MG expressed the concentration change of the reactants and products well. The reaction parameters including activation energy are reported in this paper.
A new solid acid catalyst consisting of ZrO2 supported on CaO, ZrO2/CaO was prepared by deposition of Zr alkoxide on CaO and calcination at high temperatures. A catalyst prepared by the double deposition method, ZrO2/ZrO2/CaO, was also tested. The characteristics of the catalysts were investigated for transesterification and ethanol decomposition. The transesterification activity of the ZrO2/CaO catalyst was comparable with that of proton-type zeolites. The ethanol conversion activity was similar to that of SiO2–Al2O3. Diethyl ether was not formed on the ZrO2/CaO catalyst, which showed very high selectivity for ethylene formation. The ZrO2/ZrO2/CaO catalyst showed activity for ethanol conversion even though calcined at 1373 K.
MFI type galloaluminosilicate (GaAlMFI) was coated with siliceous MFI type zeolite, silicalite-1. Silicalite-1 could be grown secondarily on GaAlMFI crystals. The silicalite-1 coating enhanced the para-xylene selectivity from 57 to 80% during aromatization of propane. The product distribution showed molecules larger than the pore size of MFI were reduced by the silicalite-1 coating, indicating that the reactions could be limited to within the pores, inhibiting the occurrence of nonselective reactions on the external surface of the zeolite crystals.