Color improvment of C9 hydrocarbon resin by hydrogenation over 2% Pd/γ‐alumina catalyst: Effect of degree of aromatic rings hydrogenation

Color improvement of commercial C₉ hydrocarbon resin (c‐C₉HR) and prepared C₉ hydrocarbon resin (p‐C₉HR) has been investigated under various hydrogenation conditions over 2% Pd/γ‐alumina catalysts. The degrees of aromatic rings hydrogenation (DHs) and molecular structure of resin were determined from nuclear magnetic resonance of ¹H and ¹³C (¹H‐NMR and ¹³C‐NMR) and Fourier transform infrared spectroscopy (FTIR) analyses. The starting c‐C₉HR presented in yellow color (Gardner color No. 8.4). Under the hydrogenation conditions used (H₂ pressure 70 bar, 250°C, and 8 h), the ethylenic proton in c‐C₉HR was completely removed, but the aromatic rings content remained unaltered and very little change in resin color was observed (Gardner color No.8.1). On the other hand, the starting p‐C₉HR contained only unsaturated aromatic proton with Gardner color No.17.1. Under similar conditions, aromatic rings in p‐C₉HR were converted to alicyclic rings, and its color was reduced to Gardner color No.5.7. By varying the DH of aromatics in p‐C₉HR, two‐step decolorization was observed in which at lower DH (≤10%) the color decreased sharply from 17.1 to 9.3, while further color reduction to 5.7 was obtained when the DH was increased to 94%. It is suggested that both color body and aromatic rings were the main sources contributing to C₉HR color. Nevertheless, color stability of the resin during heat treatment was significantly improved by hydrogenation especially at DH ≥ 50%. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of Cobalt Precursors on the Dispersion of Cobalt on MCM-41

The photocatalytic activity of titanium dioxide supported on zeolites HZSM-5, HY and H was evaluated for a novel intermolecular cyclization of ethylenediamine with propylene glycol leading to dihydropyrazine. Titanium dioxide supported on zeolites has been prepared with 2 and 5 wt% of TiO₂ by solid-state reaction, impregnation and sol impregnation methods. From the characterization by XRD, BET, EDAX and TPD of NH₃, it is deduced that in all cases titanium dioxide is in small particles of anatase on zeolites. The highest photocatalytic activity was obtained with 2 wt% TiO₂/H prepared by solid-state reaction. The acidity determined by TPD of NH₃ was found to be lower for TiO₂/H than for TiO₂/HZSM-5 and TiO₂/HY. From the above observations, it can be concluded that adsorption, acidity and structure of zeolites have an influence on the activity of supported TiO₂.     

The influence of Si-modified TiO2 on the activity of Ag/TiO2 in CO oxidation

Nanocrystalline TiO₂ and Si-modified TiO₂ with Si/Ti ratios 0.01, 0.05, 0.1, and 0.3 were prepared by the solvothermal method and employed as the supports for Ag/TiO₂ catalysts for CO oxidation reaction. The incorporation of Si into the TiO₂ lattice in the form of Ti–O–Si as revealed by FT-IR results could inhibit the agglomeration of TiO₂ crystallites, resulting in an increase of both surface area and metal dispersion. However, there existed an optimum content of Si/Ti at ca. 0.05–0.1 which resulted in an improved catalytic activity of Ag/TiO₂ in CO oxidation. Based on the O₂-temperature program desorption (O₂-TPD) results, the catalysts with appropriate amounts of Si/Ti exhibited higher amount of O₂ adsorption and much lower desorption temperature. It is suggested that the presence of Ti–O–Si promoted the formation of active oxygen species and increased the mobility of lattice oxygen so that the catalytic activity was enhanced. There was no improvement in CO oxidation activity of the Ag/TiO₂ catalyst when the Si/Ti was further increased to 0.3 due probably to the formation of amorphous SiO₂ instead of the Ti–O–Si bond.     

Impact of quenching process on the surface defect of titanium dioxide for hydrogen production from photocatalytic decomposition of water

Nanocrystalline titania was prepared by solvothermal reaction of titanium butoxide in toluene at 300 °C for 2 h. Thus obtained-powder was calcined at 300 °C in box furnace for 1 h and then quenched in various media at different temperature. The physiochemical properties of samples were investigated by using X-ray diffraction (XRD), nitrogen adsorption, CO₂-Temperature Programmed Desorption (CO₂-TPD), UV–visible scanning spectrophotometer, Transmission electron microscopy (TEM) and electron spin resonance spectroscopy (ESR) techniques. All physical properties such as phase, BET surface area and crystal size were not changed after quenching processes. While the CO₂-TPD and ESR results indicate the changing of Ti³⁺ contents on the surface of TiO₂ after quenching process. The amounts of Ti³⁺ increased as the quenching temperature decreased. Photocatalytic decomposition of water was carried out to evaluate the catalytic activity of quenched TiO₂. The activity of quenched-powder increased corresponding to the increasing of Ti³⁺ contents increased by following order: air at 77 K > air at RT > air at 373 K > 30 wt% H₂O₂ at RT = 30 wt% H₂O₂ at 373 K > H₂O at RT > H₂O at 373 K.     

Effect of Particle Size on the Hydrothermal Stability and Catalytic Activity of Polycrystalline Beta Zeolite

The effect of particle size in the range of 0.2–0.9 μ m on the hydrothermal stability of polycrystalline beta zeolites was investigated in terms of changes in BET surface areas, percent crystallinity, and framework aluminum atoms. It was found that the hydrothermal stability of beta zeolite increased with increasing particle size while the catalytic activities decreased. However, the XRD results have revealed that percent crystallinity of the hydrothermally treated beta zeolite remained relatively high (> 95%) although dealumination occurred in most cases. This high stability is due probably to small amount of Al atoms present in the unit cell of this zeolite.     

Effect of Surface Tungstate W<Superscript>5+</Superscript> Species on the Metathesis Activity of W-Doped Spherical Silica Catalysts

The high surface area W-doped spherical silica (SSP) catalysts were prepared with different sequences of W and Si addition (W–Si_(Alt), Si₁–W_2, and W₁–Si₂) by the sol–gel method with CTAB as a structure directing agent and compared with the impregnated one (W/SSP). All the catalysts exhibited high specific surface area (～?1100 m² g^?1) with a closely perfect spherical shape. The presence of surface/sub-surface tungstate W⁵⁺ species, crystalline bulk WO₃, and tetrahedral tungsten oxide species on the prepared catalysts was investigated by means of X-ray photoelectron spectroscopy depth profile analysis, X-ray diffraction, and Raman spectroscopy. Without in situ reduction by the reactants/products, tungstate W⁵⁺ species was found on the top surface of the as-prepared W–Si_(Alt) whereas for the Si₁–W₂, W/SSP, and W₁–Si₂, the W⁵⁺ appeared only on the sub-surface of the catalysts after 5 and 15 s Ar⁺ etching. The abundance of surface W⁵⁺ species is suggested to facilitate the establishment of the active tungsten carbenes and was correlated well to the catalytic activity in propene metathesis. The surface W⁵⁺-activity relationship of the WO₃-based metathesis catalysts is useful especially when the catalyst activity did not depend solely on the amount of active tetrahedral coordinated tungsten oxides.     

Comparative Study of Lewis Acid Transformation on Non-reducible and Reducible Oxides Under Hydrogen Atmosphere by In Situ DRIFTS of Adsorbed NH<Subscript>3</Subscript>

The Lewis acid transformation to Bronsted acid was investigated over the Pt/γ-Al₂O₃ hybrid catalysts in the presence of hydrogen atmosphere by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed NH₃. The changes of FTIR spectra were monitored during the introduction of hydrogen at 40 °C and atmospheric pressure for 130 min. The degrees of Lewis acid transformation were varied by addition of non-reducible (SiO₂ and Al₂O₃) and reducible (ZrO₂, TiO₂ and CeO₂) oxides to the Pt/γ-Al₂O₃ catalysts as the hybrid catalysts. According to the in situ DRIFTS, the hydrogen temperature programmed reduction (H₂-TPR), and the hydrogen temperature programmed desorption (H₂-TPD) results, the introduction of hydrogen resulted in a decrease in the amount of ammonia adsorbed on Lewis acid sites, and an increase in the amount of ammonium ions on Bronsted acid sites with time on stream. It is proposed that ammonia migration from Lewis acid sites to Bronsted acid sites occurred during the introduction of hydrogen in the presence of Pt particles when compared to the observation of only observed catalysts (without Pt particles). The addition of reducible oxides led to the high rate of Lewis acid transformation, which was higher than those of the non-reducible oxides. Weaker Lewis acid sites and higher amount of hydrogen spillover over the observed catalysts enhanced the rate of Lewis acid transformation in this study. However, the amount of Lewis acid sites at the initial stage did not play an important role in these transformations.     

Effect of Ni-modified α-Al2O3 prepared by sol–gel and solvothermal methods on the characteristics and catalytic properties of Pd/α-Al2O3 catalysts

In the present study, Ni-modified α-Al₂O₃ with Ni/Al ratios of 0.3 and 0.5 were prepared by sol–gel and solvothermal method and then were impregnated with 0.3 wt.% Pd. Due to different crystallization mechanism of the two preparation methods used, addition of nickel during preparation of α-Al₂O₃ resulted in various species such as NiAl₂O₄, mixed phases between NiAl₂O₄ and α-Al₂O₃, and mixed phases between NiAl₂O₄ and NiO. As revealed by NH₃-temperature programmed desorption, formation of NiAl₂O₄ drastically reduced acidity of alumina, hence lower amounts of coke deposited during acetylene hydrogenation was found for the Ni-modified α-Al₂O₃ supported catalysts. For any given method, ethylene selectivity was improved in the order of Pd/Ni–Al₂O₃-0.5 > Pd/Ni–Al₂O₃-0.3 > Pd/Ni–Al₂O₃-0  Pd/α–Al₂O₃-commercial. When comparing the samples prepared by different techniques, the sol–gel-made samples showed better performances than the solvothermal-derived ones.     

Effect of Support Crystallite Size on Catalytic Activity and Deactivation of Nanocrystalline ZnAl2O4-Supported Pd Catalysts in Liquid-Phase Hydrogenation

The catalytic activity and deactivation of nanocrystalline ZnAl₂O₄-supported Pd catalysts were investigated for the liquid-phase hydrogenation under mild conditions. Nanocrystalline ZnAl₂O₄ spinels with average crystallite size between 8 and 33 nm were synthesized by the solvothermal method in toluene. Higher turnover frequencies for 1-heptyne hydrogenation and less deactivation due to Pd leaching were obtained for the Pd/ZnAl₂O₄-33 nm catalyst. XPS and ESR results suggest that the presence of defects in larger crystallite size ZnAl₂O₄ resulted in higher Pd dispersion and stronger interaction between Pd and the support.     

Characteristics and Catalytic Properties of Mesocellular Foam Silica Supported Pd Nanoparticles in the Liquid-Phase Selective Hydrogenation of Phenylacetylene

Abstract  

An ultra-large pore mesocellular foam silica (MCF) was employed as a support for preparation of supported Pd catalysts for the liquid-phase selective hydrogenation of phenylacetylene. The catalysts were prepared by three different routes: (i) incipient wetness impregnation using Pd(II)acetate solution (Pd/MCF-imp), (ii) impregnation of colloidal Pd nanoparticles obtained by the solvent reduction method (Pd/MCF-col), and (iii) in situ synthesis of MCF in the presence of the Pd colloid (Pd/MCF-ss). The conventional impregnation method resulted in more agglomeration of Pd particles and partial collapse of MCF structure, hence the Pd/MCF-imp exhibited the lowest selectivity towards styrene at total conversion of phenylacetylene. Only the Pd/MCF-ss, in which most of the Pd nanoparticles were encapsulated by the silica matrix, was found to retain high styrene selectivity (>80%) after complete conversion of phenylacetylene. Comparing to the other highly efficient Pd catalysts reported in the literature under similar reaction conditions, it can be emphasized that coverage of Pd surface by the support produces great beneficial effect for enhancing styrene selectivity, regardless of the type of supports used (i.e., TiO₂, carbon nanotubes, or mesostructured silica).