Papers by Author: Guo Xian Yu

Abstract: The effect of steam, fed to the fixed-bed microreactor reactor, on the oxidative dehydrogenation of cyclohexane over Mg₃(VO₄)₂ catalyst was reported. The catalyst characterization results showed that the crystal structure, the electron cloud distributions of the active species and the oxygen species, and the reducibility of the active species are not influence by the introduction of steam. It was observed that steam added to the oxidative dehydrogenation of cyclohexane competes for sites required for gas-phase oxygen activation, which catalyst lattice oxygen utilization is not affected. The shorter residence time and the competition for sites with oxygen causes a decrease in cyclohexane conversion and a corresponding increase in selectivity to cyclohexene.

Abstract: The MDEA-PZ binary system and the MDEA-PZ-MEA/DEA/ETA/TETA ternary system were used to absorb CO₂ from the simulated flue gas. The experimental results showed that the best performance of the absorption of CO₂ was achieved under the mass ratio of MDEA to PZ of 10/4 in the MDEA-PZ binary system. In the MDEA-PZ-MEA/DEA/ETA/TETA ternary system, due to the different molecular structure of the additives, the absorption performance of CO₂ was determined as follows: MDEA-PZ-TETA>MDEA-PZ-ETA>MDEA-PZ-MEA>MDEA-PZ-DEA. In the MDEA- PZ- TETA ternary system, the better absorption performance could be reached at the volume ratio of MDEA-PZ to TETA of 1:2. Moreover, it was indicated that there was a weakly negative interaction among MDEA, PZ and TETA.

Abstract: A Mg₃(VO₄)₂ catalyst was synthesized and investigated for the oxidative dehydrogenation of cyclohexane to cyclohexene. Integral measurements were performed to determine the reaction network and products distribution, and differential measurements for kinetic investigations. The kinetic study indicated the oxidative dehydrogenation of cyclohexane to cyclohexene follow a parallel-consecutive network. The power law kinetic model was considered as a rough approximation of the experimental results. The rate constants, which included the activation energies, the pre-exponential factors as well as the orders of cyclohexane and oxygen, were evaluated.

Abstract: Oxidative dehydrogenation of cyclohexane was studied over three pure Mg-V-O catalysts, which are Mg₃(VO₄)₂, Mg₂V₂O₇ and MgV₂O₆, respectively. Catalysts were prepared via citric acid complexation and characterized by N₂-adsorption, XRD, FT-IR, NH₃-TPD and H₂-TPR techniques. Among the pure magnesium vanadates, Mg₃(VO₄)₂ has the isolated active sites, weakly basic surface and lower reducibility of the metal cations, and could be recognized as the catalytic active phase. Mg₃(VO₄)₂ catalyst exhibited a better catalytic performance, on which a cyclohexene selectivity of 41.5% at cyclohexane conversion of 15.5% was obtained.

Abstract: Effects of ytterbia for Pt-SO42-/ZrO2-Al2O3-Yb2O3 (PSZAY) catalysts in n-hexane hydroisomerization were investigated. It was elucidated that the introduction of ytterbia into Pt-SO42-/ZrO2-Al2O3 (PSZA) increased both the surface area and the number of active sites, resulting in a higher n-hexane isomerization activity. At the same time the catalyst stability has also been markedly increased by alleviating the sulfur loss and by stabilizing ZrO2 tetragonal crystalline structure.

Abstract: Transition metal-modified carbon-based adsorbents were prepared by impregnating activated carbon with solutions of copper, cobalt or nickel chloride or nitrate. The mixtures were dried and then calcined under nitrogen stream. The surface metal species were analyzed by XRD technique and the surface oxygen-containing groups were characterized by FTIR. Their adsorption capacities for dibenzothiophene (DBT) were measured by using DBT-containing n-octane solution as model oil. Experimental results show that the metal species on the carbon surface could be controlled by the calcination process under nitrogen atmosphere. Both the transition metal precursors and kinds of metal species on the carbon surface have significant effects on DBT adsorption capacity.

Abstract: Rice hull (designated with RH) was activated by phosphoric acid to prepare an adsorbent for the removal of sulfur-containing compounds from diesel fuel. Adsorption tests for both, a 300 µg.g-1 dibenzothiophene (DBT)-containing n-octane solution using as model oil and a commercial hydro-treated diesel fuel, were performed to elucidate the effect of varying phosphoric acid to RH ratio, treating temperature and the removal of silica from the adsorbent on the combination of the textural structure, surface chemical property and adsorption capacity. It was indicated that high surface area and micro-pore volume of the adsorbent favored the adsorption of DBT and its derivatives. Richening of oxygen-containing compounds on the adsorbent surface was advantageous to the adsorption and removal of DBTs. At a phosphoric acid and RH weight ratio of 3:1 by using a two-step treatment, a satisfactory adsorbent with an adsorption capacity of 28.89 mg S/g was successfully prepared. If the silica in the adsorbent was further removed, the product exhibited the highest performance, reaching 30.43 mg S/g for the model oil and 21.79 mg S/g for the commercial diesel fuel. Both the textural structure and the surface chemical property like acidic groups of a RH-based adsorbent play important roles in its adsorption behaviors, and the formation of donor-acceptor complexes between surface acidic groups and DBT may probably benefit DBT adsorption capacity.

Abstract: Phosphotungstic acid (HPW) supported on activated carbon (AC) combined with hydrogen peroxide formed an oxidative desulfurizaiton (ODS) system to oxidize sulfur-containing compounds in diesel fuel. Dibenzothiophene (DBT) dissolved in n-octane was selected as a model feedstock for studying this new ODS system. The HPW/AC catalysts were characterized with XRD, FTIR and N2 adsorption-desorption measurements. HPW was highly dispersed on the surface of carbon support. It was found that the DBT adsorption capacity decreased from 42 mg S/g to 33.13 mg S/g as HPW loading amount increased from 0 to 15 wt.%. Oxidative removal of DBT in the model oil significantly increased with increasing HPW loadings on the support from 0 to 10 wt.%. 100 % DBT was removed by using the catalysts with HPW content higher than 10 wt. %. At 80 °C, oxidative removal of DBT reached 100 % after 40 min of reaction when O/S molar ratio ranged from 4 to 10.

Abstract: Two types of mesoporous Si-MCM-41 materials were synthesized via a cationic surfactant template method using different Si-precursors. The materials obtained were characterized by FTIR, XRD, BET, TEM and 29Si MAS-NMR techniques. When fumed silica was used as Si precursor, a Si-MCM-41-I solid with wormhole-like pore topologies was obtained. However, when tetraethylorthosilicate (TEOS) was used as Si precursor, a mesoporous Si-MCM-41-II solid with hexagonal arranges and a long-range ordered structure could be obtained. These two kinds of mesoporous materials had a uniform pore size distribution with an average pore diameter within 2.3-2.8 nm. Rather weak Lewis acid sites were formed on both the Si-MCM-41 samples prepared by the two methods.

Abstract: Lanthanum (La) nano-films prepared by a self-assembled technique on a silicone-based material surface, was studied by using an all-round functional Turbiscan LAB stability analyzer and X-ray fluorescence analysis (XRF) as well as atomic force microscope (AFM). La content introduced in the assembled nano-film reached a maximum at pH value between 5 and 6. In the preparation of colloidal sol, no phase separation took place at 60 °C where the colloidal particles uniformly and stably dispersed in the solution. The optimum topographic feature was observed after 24 hours, whence self-assembled process was performed. The particle dispersion of the assembled film was uniform and compact at the optimum EDTA to La molar ratio 0.5.