Hydrogenation of MTHPA to MHHPA over Ni-based catalysts: Al2O3 coating, Ru incorporation and kinetics.

Because of its excellent performance, methyl hexahydrophthalic anhydride (MHHPA) is a new anhydride-based epoxy resin curing agent after methyl tetrahydrophthalic anhydride (MTHPA). To improve the activity and stability of conventional RANEY® nickel catalysts in the catalytic hydrogenation of MTHPA to MHHPA reaction, RANEY® nickel encapsulated with porous Al2O3 and alumina-supported Ni-Ru bimetallic catalysts were designed and synthesized in this study. The physicochemical properties and surface reactions over the catalysts were characterized by N2 adsorption and desorption, X-ray diffraction (XRD), hydrogen temperature-programmed reduction/desorption (H2-TPR/TPD), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and in situ diffuse reflectance infrared Fourier transformations spectroscopy (DRIFTS). The kinetic model of MTHPA hydrogenation over NiRu/Al was established and the parameters were estimated using the least-square method. The results showed that the encapsulation of porous Al2O3 on the surface of RANEY® nickel enhanced the stability of the Ni skeleton and the adsorption ability of the reactant molecules, which improved its activity for the hydrogenation reaction. The introduction of Ru improved the dispersion and stability of metallic Ni, which greatly increased the conversion ability towards MTHPA hydrogenation, but it had a trend to cause C[double bond, length as m-dash]C bond transfer at lower temperatures, increasing the hydrogenation difficulties. The kinetic results based on Ni-Ru bimetallic catalyst showed that the MTHPA hydrogenation reaction rate was first-order with respect to MTHPA concentration and 0.5-order with respect to hydrogen partial pressure, and the apparent activation energy of the hydrogenation reaction was 37.02 ± 2.62 kJ mol-1.

Melting Characteristics of Coal Ash and Properties of Fly Ash to Understand the Slag Formation in the Shell Gasifier.

The flow temperature (FT) of the coal ash from the Liuqiao no. 2 mine in North Anhui Province (C00) is too high (∼1520 °C) to fit the Shell gasifier due to its relatively high content of SiO2 and Al2O3. To solve this problem, a series of coals were blended with C00 with different ratios, and the relations between FT and the ash composition were investigated. The coal ash was analyzed by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy-EDX to elucidate the mechanism of the improved ash fusion performance and the slag formation in the waste heat boiler of the gasifier. It is shown that FT is relevant to the coal ash compositions as well as the structures formed at high temperatures. The existence of alkaline oxides (CaO, MgO, and Fe2O3) decreases the coal ash FT to a low level. The FT can decrease to <1350 °C to cater to the Shell gasifier by blending C00 and C03 with a mass ratio of 4:6 owing to the plentiful alkaline oxides in C03. The FTIR results indicate that the high flow temperature of C00 is attributed to the formation of mullite at high temperatures. The coal blending with various ratios changes the compositions of CaO, MgO, and Fe2O3, which can form some low-melting-point eutectic compounds with SiO2 and Al2O3 under high temperatures, inhibit the formation of mullite, and thus decrease the ash FT. The coal ash FT was found to have a good linear relation with the ash compositions, which can sever as a reference to the coal blending. According to the model parameters, it is shown that Mg has the most significant promoting effect on the decrease in FT of the coal ash. The caking tendency of fly ash increases with the rising Ca content and an excessive Ca-based fluxing agent used in the coal blending will lead to the aggregation of the Ca-rich clasts around the fly ash particle, resulting in the plugging of the waste heat boiler in the gasifier. Therefore, the Mg-based fluxing agent is more promising to improve the ash fusion performance and reduce the caking tendency of the coal fly ash.

Ru-Ni bimetallic catalysts for steam reforming of xylene: effects of active metals and calcination temperature of the support.

A series of Ru and Ni supported catalysts were prepared and their catalytic performance was evaluated in the steam reforming of xylenes. The effects of active metals, active metal loading sequence, and the calcination temperature of the support on the catalyst activity and stability were investigated. The bimetallic 2Ru → 15Ni catalyst shows much higher activity and stability than the monometallic 2Ru and 15Ni catalyst owing to the synergic effect of Ni and Ru. The 2Ru → 15Ni catalyst has the least coke deposition owing to its high conversion performance and much less coke precursor being formed on the catalyst surface. After decoking, most of the small-sized pores cannot be recovered because of the pore collapse under severe hydrothermal conditions. o-Xylene has the lowest reactivity due to electronic and steric effects. Besides the steam reforming reaction, demethylation and C-C cracking are also observed, forming benzene and toluene. The catalyst with a loading sequence of 15Ni → 2Ru shows high activity at low temperatures (550-600 °C), but undergoes an activity drop at high temperatures (625-650 °C) because the Ni sintering at high temperatures greatly affects the state of Ru on the catalyst. The catalyst with a loading sequence of 2Ru → 15Ni has an advantage at high temperatures owing to its better sintering resistance. The simultaneously loaded 2Ru ↔ 15Ni catalyst shows the lowest activity. The high calcination temperature of the support enhances the catalyst stability by eliminating the small-sized pores before reaction; on the other hand, the elimination of pores decreases the dispersion of the active metals. The 2Ru → 15Ni catalyst calcined at 1000 °C balances the active metal dispersion and resistance to sintering under severe hydrothermal conditions, showing the best activity and stability. The catalyst calcined at 1000 °C has the best coke resistance with only 0.166 g gcat -1 of coke formation after the 24 h durability test. The DTG results indicate that the carbon formed on the catalysts is mainly graphitic carbon.

SO4 2-/ZrO2 as a Solid Acid for the Esterification of Palmitic Acid with Methanol: Effects of the Calcination Time and Recycle Method.

Two types of SO4 2-/ZrO2 solid acid catalysts with various calcination times were prepared via incipient wetness impregnation of (NH4)2SO4 to hydrothermally synthesized ZrO2 and subsequently employed to catalyze the esterification of palmitic acid with methanol. The resulting catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and temperature-programmed oxidation (TPO) to elucidate their physicochemical properties, morphology, and deactivation mechanism. A calcination procedure is required to transform the amorphous ZrO2 into the crystal form. Both chelating and bridged bidentate SO4 2- coordinate with the ZrO2 surface. The calcination at 600 °C could well eliminate the water in the catalyst and a further higher temperature would accelerate the loss of SO4 2-. Long-time calcination also decreases the catalytic activity due to the transformation of monoclinic ZrO2 into tetragonal one and the slow leaching of SO4 2-. The catalytic activity increases with increasing catalyst loading amount, reaction temperature, and molar ratio of palmitic acid to methanol, while the heating temperature over 65 °C and excess methanol amount are unfavorable to the esterification reaction due to the low-boiling-point methanol and attenuation of the palmitic acid concentration. It appears that the reaction conditions of 65 °C, 6 wt % catalyst, 25:1 of methanol to palmitic acid, and 4 h reaction time are economically optimal under atmospheric pressure. The catalyst could not be well regenerated by the ultrasonic methanol washing method because of refractory organic residues. The catalyst activity could be well recovered without major activity loss by the calcination at 600 °C for 1 h. The catalyst deactivation is due to contamination by the refractory organic residues in the catalyst as well as by the leaching of SO4 2-, and thus both the calcination temperature and time should be strictly controlled to achieve a better catalyst lifetime.