Hakze Chon

Catalytic activity and coke resistance in the carbon dioxide reforming of methane to synthesis gas over zeolite-supported Ni catalysts

Abstract The CO2 reforming of methane to synthesis gas was performed over pentasil-type zeolite-supported Ni catalysts. High activity with high resistance to coke in the catalysts was confirmed by obtaining near equilibrium conversions of CO2 and methane as well as near equilibrium yields on CO and H2 for over 140 h of reaction. Coke deposition on the catalysts for the CO2-reforming reaction was remarkably diminished with the addition of alkaline promoters such as K and Ca oxides. This was attributed to the formation of carbonate species on alkaline promoters, mainly Ca, located adjacent to Ni sites and to the dissociative adsorption of CO2 on an Ni surface by the addition of alkaline promoters.

Hydrogenation of furfural over copper-containing catalysts

Abstract Furfuryl alcohol is the main product of the vapor-phase hydrogenation of furfural over copper-containing catalysts such as copper-chromium oxide and palladium-loaded CuY. The amount of furan adsorbed on CuY increases with increasing degree of Cu(II) ion exchange. The evidence of interaction between Cu(II) ion and the furan ring is demonstrated in the ir and EPR spectra. High selectivity to furfuryl alcohol and the absence of tetrahydrofurfuryl alcohol formation over copper-containing catalysts is interpreted in terms of the interaction between Cu(II) ion and the furan ring of furfural preventing the furan ring from being hydrogenated. This interaction also explains the enhancement of conversion to furfuryl alcohol on PdCuY. Here the active site for the selective formation of furfuryl alcohol is the Cu(II) ion interacting with the furan ring while Pd activating the hydrogen.

Synthesis and characterization of the vanadium-incorporated molecular sieve VAPO-5

Abstract The vanadium-incorporated molecular sieve VAPO-5 was synthesized hydrothermally and characterized by X-ray diffraction, electron paramagnetic resonance, thermogravimetric analysis, diffuse reflectance spectroscopy, chemical analysis and adsorption techniques. It seems that the vanadium is incorporated mainly as V 4+ in the as-synthesized VAPO-5 framework. The vanadium in VAPO-5 exists in a well dispersed state and shows redox properties, changing its oxidation state readily between V 4+ and V 5+ .

Hall effect studies of oxygen chemisorption on zinc oxide

Dual ac Hall effect measurements of the chemisorption of oxygen on gallium-doped zinc oxide have shown that oxygen is chemisorbed primarily as O2− between 100 ° and about 180 °C, and as O− above about 230 °C.

Isomorphous substitution of iron ions into aluminophosphate molecular sieve, AIP04-5

Abstract FAPO-5 molecular sieves synthesized with Fe(II) and TEAOH and differing in iron content have been characterized by using various physicochemical methods to elucidate the incorporation of the iron ions into the aluminophosphate matrix. In as-synthesized FAPO-5, a large portion of Fe(III) ions are located in the framework position of AIPO 4 -5, and Fe(II) ions are introduced in place of Al(III) ions in the form of Fe(II)TEA + . Fe(II) ions are oxidized to Fe(III) while remaining in the framework position in the course of calcination to remove the template. In the case of Fe-silicate ZSM-5, some of the Fe(III) ions located in the framework seem to be removed after the calcination.

Diffusion of Cyclohexanes in ZSM-5 Zeolites

Diffusion coefficients have been measured for the diffusion of cyclohexane and alkylcyclohexanes ranging from methyl-to pentylcyclohexane in ZSM-5-type zeolites using the samples of flat plate-like crystallite. The uptake curves of cyclohexanes by these samples are considered to represent primarily the diffusion of cyclohexanes into the straight channel. The diffusion coefficient of cyclohexane at 377 K was 4.8 {times} 10{sup {minus}13} cm{sup 2}/sec and they were 9.9 {times} 10{sup {minus}13}, 2.3 {times} 10{sup {minus}13}, 2.6 {times} 10{sup {minus}13}, 3.8 {times} 10{sup {minus}13}, and 5.4 {times} 10{sup {minus}13} cm{sup 2}/sec for methyl-, ethyl-, n-propyl, n-butyl-, and n-pentylcyclohexane, respectively. The diffusion coefficients of monosubstituted n-alkylcyclohexane showed a minimum at ethylcyclohexane and increased steadily as the chain length got longer. The length of the ethylcyclohexane molecule is comparable to the intersection space and the sharp decrease in the diffusion coefficient can be interpreted in terms of the cage effect. The diffusion coefficient of the t-1,4-dimethylcyclohexane was two orders of magnitude larger than that of ethylcyclohexane although they have about the same molecular length and kinetic diameter. This may be attributed to the methyl-methyl interaction resulting in a favorable orientation for diffusion through the intersection space.

Interaction of furans and thiophenes with Cu (II) — exchanged ZSM-5 and Y zeolites

Abstract The formation of radicals on furan and thiophene and their methyl derivatives of CuZSM-5 and on CuY zeolites was studied by EPR technique. In some cases, stable monomer radicals of furans and thiophenes were observed on CuZSM-5, whereas the dimeric radicals were observed mainly on CuY. The channel structure of the zeolite seemed to affect the formation of radical species.

The influence of metal ions on the synthesis of MeAPO-5 (Me-Co, Mg) in the presence of acetate ions

Abstract Metal-substituted type 5 aluminophosphate structures have been prepared hydrothermally in a buffer solution consisting of acetic acid and a high concentration of template. The acetate ion added to the reaction mixture decreases the interaction of the metal ions with the gel and keeps the initial pH of the mother liquor. There was almost no change in the pH of the reaction mixture during the preparation. The most suitable pH range to synthesize single crystals of MeAPO-5 (Me = Co, Mg) was found to be around pH 5.5. The morphologies of the as-synthesized MeAPO-5 crystals were strongly dependent on the pH of the solution. The size of the crystals increased with increasing metal contents. Owing to the roles of acetate ions, MeAPO-5 crystals were obtained at high concentrations of template and metal ion. Increasing the amount of water and reducing the reaction temperature resulted in the formation of CHA-type structures.

Synthesis of aluminophosphate-based layered compounds using Al(OH)3

Abstract Large novel anionic aluminophosphate-based layered compounds were synthesized using Al(OH)3 as an aluminum source and cyclohexylamine as an organic template. The characterization studies by means of XRD, SEM. thermal analysis, MAS NMR, FT-IR and elemental analysis showed that cobalt ions were substituted for Al in the tetrahedral framework and that protonated cyclohexylamine cations were intercalated as a double layer form between macroanionic AlPO sheets. The removal of cyclohexylamine by the calcination process resulted in a collapse of the layered structure into an amorphous phase. The empirical formula of the AlPO layered compound was generally 3.4 C6H12NH2 [Al3H3P4O16], showing an unusual molar ratio of an Al: P = 0.75 and higher content of organic amines than that of AlPO molecular sieves.

AMMOXIDATION OF TOLUENE OVER CUNA-ZSM-5

Abstract The ammoxidation reaction of toluene over CuNa-ZSM-5 catalysts has been investigated. CuNa-ZSM-5 showed the best activity and selectivity for benzonitrile formation among [MnII, CoII, NiII, CuII, ZnII and AgI] ion-exchanged CuNa-ZSM-5. It was found that CuII in the zeolite matrix readily forms an ammine complex with ammonia and a charge transfer complex with toluene and, when ammonia and toluene were added concurrently, [CuII (ammonia) (toluene)] complex was formed and remained at the typical reaction condition. Changes in the reaction pattern for the ammoxidation of toluene under the various reaction conditions can be explained in terms of the stability of the [CuII (ammonia) (toluene)] complex. We tentatively formulated the mechanistic scheme for the ammoxidation reaction of toluene over the CuNa-ZSM-5 catalyst. The present work shows that the [CuII (ammonia) (toluene)] complex formed in the CuNa-ZSM-5 seemed to offer a new reaction pathway which was different from those over the metal oxide catalysts.