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 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.     

Catalytic performance improvement of styrene hydrogenation in trickle bed reactor by using periodic operation

We investigated the catalytic performance improvement of styrene hydrogenation in a trickle bed reactor by using periodic operation. The effects of cycle period and split on relative conversion, which is defined as styrene conversion obtained from periodic operation over that from steady state operation, were examined at various operating conditions including gas and average liquid flow rates, pressure and temperature. The experimental results reveal that both cycle period and split have strong influence on the catalytic performance. The fast mode (short cycle period) is a favorable condition. The improvement by the periodic operation becomes less pronounced for operations at high average liquid flow rate, pressure and temperature. From this study, a maximum improvement of styrene conversion of 18% is observed.     

Ethylene and mixed 2-butene cis/trans isomers metathesis: Influence of lanthanum as a second metal on the WO3/SiO2 catalysts

Lanthanum (0.5, 0.6, 0.75, 0.9 and 1 wt%) was added as a second metal on the 9 wt% WO₃/SiO₂ catalysts by the incipient wetness impregnation method. The catalysts were tested in the metathesis reaction of ethylene and 2-butene using either pure 2% trans-2-butene and the mixture of 1% cis- and 1% trans-2-butene as the reaction feed and were characterized by X-ray diffraction (XRD), nitrogen physisorption (BET), inductively coupled plasma optical emission spectrometry (ICP-OES), scanning electron microscopy, ion-exchange titration, FT-Raman, ammonia temperature programmed desorption (NH₃-TPD) and reactant temperature programmed desorption (reactant-TPD). An optimum lanthanum loading at 0.5 wt% could improve dispersion of tungsten active phase and adsorption properties of the reactants on the catalysts. The adsorption of the mixed cis/trans-2-butene isomer was much improved on the La-WO₃/SiO₂ catalysts with 0.5 wt% La.     

Enhanced Stability and Propene Yield in Propane Dehydrogenation on PtIn/Mg(Al)O Catalysts with Various In Loadings

The dehydrogenation of propane on In-promoted Pt (0.3 wt% Pt) supported on hydrotalcite Mg(Al)O with different In loadings (0.2–1.0 wt% In) was investigated at 550 °C atmospheric pressure. All the bimetallic PtIn/Mg(Al)O showed higher propane conversion and propene selectivity than the Pt/Mg(Al)O with Pt0.8In exhibited the best catalytic performances with 97.5% propylene selectivity and 27.5% yield after 5 h time-on-stream. The addition of In to the monometallic Pt catalyst could reduce the acidity strength especially the strong acid site. As revealed by the H₂-TPR and XPS results, addition of In by impregnation on Pt/Mg(Al)O also led to the formation of metallic In and PtIn alloy, which greatly enhanced the catalyst activity and reduced coke formation on the support. Nevertheless, excessive In loading (i.e., Pt1.0In) resulted in a descending trend of catalyst activity compared to the Pt0.8In, due probably to the large amount of metallic In being formed, which was disadvantageous in propane dehydrogenation.