Youchang Xie

Support effects on the catalytic behavior of NiO/Al2O3 for oxidative dehydrogenation of ethane to ethylene

Six representative Al2O3 supports with different specific surface areas and pore volumes were used to prepare NiO/Al2O3 catalysts with two NiO loadings. Oxidative dehydrogenation of ethane (ODE) to ethylene was investigated over these catalysts. The yield of ethylene was found to be approximately proportional to the pore volume/surface area ratio of the support used for that catalyst. X-ray diffraction analysis (XRD), TEM and H2-TPR were employed to characterize their structure differences. It was found that the physical properties of the Al2O3 supports were crucial to the dispersion of NiO. More large crystal NiO was found on the Al2O3 supports with lower pore volume, while more highly dispersed NiO was formed on the Al2O3 supports with higher pore volume. An interpretation based on the pore volume of the supports and the physical properties of salt precursors was proposed.

Monolayer dispersion of MoO3, NiO and their precursors on γ-Al2O3

Abstract The dispersion capacities of MoO 3 , NiO and their precursors on the surface of γ-Al 2 O 3 are studied by XPS and XRD techniques. As a relatively low melting point oxide, MoO 3 gives a dispersion capacity higher than its precursor molybdate based on mole of MoO 3 on γ-Al 2 O 3 . Dispersion capacities of molybdate on γ-Al 2 O 3 depend on the pH of molybdate solution used for impregnation while the dispersion capacity of MoO 3 on γ-Al 2 O 3 is independent of its precursors. As a high-melting point oxide, the dispersion capacity of NiO based on mole of NiO is the same as that of its precursor. By one-step impregnation, dispersion capacity of nickel nitrate and its derived NiO on γ-Al 2 O 3 is larger than that of nickel acetate and its derived NiO. This difference can be attributed to the larger size of nickel acetate molecule. The utmost dispersion capacity of NiO on γ-Al 2 O 3 is achieved through one-step impregnation when nickel nitrate is used as the precursor, while the same capacity can only be achieved through multiple impregnation when nickel acetate is used as the precursor.

Zeolites modified by CuCl for separating CO from gas mixtures containing CO2

Although zeolites such as NaY and 13X adsorb CO2 much more than CO, the adsorption amount of CO2 and CO can be reversed if the zeolites are modified with CuCl. When zeolite NaY or 13X is mixed with CuCl and heated, high CO adsorption selectivity and capacity can be obtained. Isotherms show the adsorbents have CO capacity much higher than CO2. This is because CuCl has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuCl can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO2 adsorption. The monolayer dispersion of CuCl is confirmed by XRD and EXAFS studies. The loading of CuCl on the zeolites has a threshold below which the CuCl forms monolayer after heating and crystalline phase of CuCl can not be detected by XRD. An adsorbent of CuCl/NaY with CuCl content closed to the monolayer capacity shows very high CO selective adsorbability for CO2, N2, H2 and CH4. At temperature higher than room temperature, the adsorbent has even better CO selectivity for CO2. Using the adsorbent, a single-stage 4 beds PSA process, working at 70°C and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%.

An important principle for catalyst preparation—spontaneous monolayer dispersion of solid compounds onto surfaces of supports

Spontaneous monolayer dispersion of oxides and salts onto supports is quite a widespread phenomenon and an important principle for the preparation and design of heterogeneous catalysts. This paper summarizes the main results developed in our laboratory. It contains the following points: (1) Preparation of highly active catalysts by dispersing active components on supports as a monolayer. (2) Thermal dispersion of active components onto supports as monolayer can be a simple method to make some catalysts. (3) Monolayer-dispersed oxides or salts play a role as surface modifiers. (4) Monolayer-dispersed oxides or salts on supports are better precursors of supported metal catalysts. (5) Regeneration of supported metal catalysts based on spontaneous monolayer dispersion of oxide and salt of the metals. (6) Hindering sinter of supports with monolayer-dispersed oxide or salt to make catalysts with very high surface area. (7) Modification of zeolites by spontaneous dispersion of oxides or salts to zeolites.

Preparation and Catalytic Activity of Monolayer-Dispersed Pt/Ni Bimetallic Catalyst for C=C and C=O Hydrogenation

Abstract The monolayer-dispersed Pt/Ni bimetallic catalyst was prepared through a simple replacement reaction, and its catalytic activity for the hydrogenation of cyclohexene, styrene, acetone, and butyl aldehyde was also tested. The Pt/Ni catalyst that was prepared by the replacement reaction showed much higher activity than Pt/Ni and Pt/Al 2 O 3 catalysts with the same Pt loading prepared by the conventional impregnation method.

Lean NOx reduction over Sn1−xZrxO2 solid solutions

SnO2-ZrO2 binary oxide solid solution was found to be a novel and good catalytic system for the selective reduction of NO by propene in the presence of oxygen. The NO conversion over SnO2-ZrO2 binary oxides changed with SnO2 content, and was the highest at about 60wt% SnO2. At 350°C, 77% conversion of NO to N2 was obtained for a feed of He stream with 1186ppm NO, 948ppm propene and 2.23% O2 at a space velocity of 15,000h−1. XRD analysis showed that uniform solid solutions with cassiterite phase were found for the SnO2 rich Sn1−xZrxO2 samples, while monoclinic and tetragonal ZrO2 phases were formed for the ZrO2 rich samples. TPR measurements suggest the introduction of Zr ions into SnO2 lattice can lead to the decease of hydrocarbon oxidation capacity and the formation of new easier reduction oxygen, which may be beneficial to the reactivity enhancement of NO conversion. The sample with composition in the intersection point of the two kinds of solid solutions (Sn0.55Zr0.45O2) presented as an amorphous phase and showed the highest activity. The solid solution catalysts could sustain moderate activity after a calcination at 800°C, in the presence of high O2 partial pressure or in the presence of 10% water.

TPR of Pd/MnO2 and Pd/Fe2O3 systems—effects of hydrogen spillover

Temperature programmed reduction of Pd/MnO 2 and Pd/Fe 2 O 3 systems were investigated. The results show that the presence of Pd lowers the reduction temperature of MnO 2 and Fe 2 O 3 due to hydrogen spillover from Pd to the oxides. Thus developed oxygen getter Pd/MnO 2 can be regenerated at lower temperature and can absorb more oxygen at room temperature than the traditional oxygen getter.

Dispersion of Na2CO3 on γ-Al2O3 and the threshold effect in flue-gas desulfurization

Na 2 CO 3 can disperse onto the surface of γ-Al 2 O 3 and form a quite complete monolayer. The adsorption capacity of SO 2 on Na 2 CO 3 /γ-Al 2 O 3 increases with Na 2 CO 3 loading, and reaches a maximum at the dispersion threshold. When the loading is below the threshold, the adsorption is in company with oxidation of SO 2 , and the regeneration recovery percentage of the adsorbent is beyond 60%. However, as the loading is at the threshold or higher, the adsorption is only an acidic-basic interaction and the regeneration recovery percentage is much lower. With due consideration for all concerned, the chosen Na 2 CO 3 loading should enable Na 2 CO 3 in the sample to cover the greater part, but not the whole surface of γ-Al 2 O 3 .

Preparation of Nanometer Magnesia with High Surface Area and Study on the Influencing Factors of the Preparation Process

Abstract Three kinds of MgC 2 O 4 ·2H 2 O were prepared by the precipitation method with different raw materials, and MgO with high surface area was obtained via thermal decomposition of MgC 2 O 4 ·2H 2 O in different atmospheres. The precursor MgC 2 O 4 ·2H 2 O and as-prepared MgO were characterized by XRD, BET, TEM, and TG-DTA measurements. It was found that using Mg(CH 3 COO) 2 ·4H 2 O and H 2 C 2 O 4 ·2H 2 O as the starting materials and calcining the precursor MgC 2 O 4 ·2H 2 O in flowing dry gas are the key factors to obtain high surface area for MgO. The MgO prepared at the optimum condition is composed of nanocrystals with a size of about 4–5 nm and forms a wormhole-like porous structure with a specific surface area of 534 m 2 ·g −1 after calcining at 520 °C. In addition, the MgO has good thermal stability; after being calcined at 650 °C and 800 °C for 2 h, its surface area is still 229 m 2 ·g −1 and 134 m 2 ·g −1 , respectively.

Phosphorous-Modified TiO2 with Excellent Thermal Stability and Its Application to the Degradation of Pollutants in Water

The phosphorous-modified TiO2 (P-TiO2) was synthesized by a hydrothermal method. The as-prepared P-TiO2 was evaluated for the degradation of methylene blue, the dechlorination of 4-chlorophenol, and the inactivation of Escherichia coli. In all these experiments, P-TiO2 shows superior activity compared with pure TiO2 and even better activity than the commercially available P25 in most cases. By carrying out methylene blue degradation in the presence of different scavengers, ·OH radicals were found to be the dominant reactive oxidizing species. The excellent performance of P-TiO2 was correlated with its pronounced ability to generate ·OH radicals under illumination. We also found that P-TiO2 is extraordinarily stable against annealing. Its transformation from anatase to rutile does not occur until calcination as high as 950 °C. This phase transformation is retarded since the phosphate species on the surface of the particles acts as a barrier to grain boundary nucleation. This peculiar feature of P-TiO2 gives it reliable performance during water decontamination even after calcination at 900 °C since it retains a 100% anatase phase at this stage.