Chang-Lin Chen

Aqueous-phase deoxygenation of glycerol to 1,3-propanediol over Pt/WO3/ZrO2 catalysts in a fixed-bed reactor

Deoxygenation of glycerol in aqueous medium catalyzed by Pt/WO3/ZrO2 at relatively low temperatures (110–140 °C) under hydrogen pressure range from 2 to 5 MPa in a fixed-bed continuous-flow reactor gives 1,3-propanediol (1,3-PDO) and n-propanol (n-PrOH) as the predominant products, indicating high selectivity for deoxygenation of the secondary hydroxyl group over the primary hydroxyl groups of the glycerol. The optimum catalyst was prepared by calcination of WO3/ZrO2 at 700 °C and loading of 3.0 wt% Pt with W content of 10 wt%. The effect of reaction temperature, hydrogen pressure and initial water content were evaluated to find the optimum reaction conditions. The glycerol conversion and the yield of 1,3-PDO greatly depended on these factors. At 130 °C, 4 MPa and 70.2% conversion, the yield of 1,3-PDO was up to 32.0% (1,3-PDO/1,2-PDO = 17.7). The proposed mechanism for glycerol deoxygenation in aqueous medium over Pt/WO3/ZrO2 is an ionic pathway involving proton and hydride ion transfer steps.

Sulfated zirconia catalyst supported on MCM-41 mesoporous molecular sieve

Sulfated zirconia (SZ) was supported on siliceous hollow tubular MCM-41 mesoporous molecular sieve by using a one-step incipient wetness impregnation method with zirconium sulfate as the precursor. The SZ/MCM-41 catalyst was obtained by thermal decomposition of the precursor in air. The resultant catalyst was characterized with various techniques, such as nitrogen physisorption, X-ray diffraction, SEM, and TEM. It was shown that the well-ordered channels of MCM-41 support arranged in hexagonal arrays while the hollow tubular morphology was retained. Both tetragonal and monoclinic phases of zirconia were developed in the catalysts. With the addition of a proper amount of aluminum as a promoter, resulting in catalyst SZA/MCM-41, the transformation of zirconia from metastable tetragonal phase to monoclinic phase was retarded. The catalytic activity of SZA/MCM-41 catalyst in the isomerization of n-butane was dramatically improved in comparison to the activities of SZ/MCM-41 or SZA/silica.

Direct impregnation method for preparing sulfated zirconia supported on mesoporous silica

A new method has been developed to prepare sulfated zirconia (S–ZrO2) supported on mesoporous silica. With direct exchange of metal containing precursors for the surfactants in the as-synthesized MCM-41 materials, the problem of fill-up of the mesoporous structure was avoided and high sulfur content was achieved. By using this method, the composite of S–ZrO2/MCM-41 with ZrO2 content higher than 60 wt.% can be easily obtained without serious blockage of the pore structure of MCM-41. Nevertheless, the pore size and pore volume of the resultant S–ZrO2/MCM-41 composites were found to vary markedly with the loading of ZrO2. The strong acidic character of the obtained composites was examined by using them as catalysts in n-butane isomerization. Introduction of other metals such as aluminum as promoter into S–ZrO2/MCM-41 can be easily conducted by the direct impregnation method.

Catalytic behavior of alumina-promoted sulfated zirconia supported on mesoporous silica in butane isomerization

Alumina-promoted sulfated zirconia was supported on mesoporous molecular sieves of pure-silica MCM-41 and SBA-15. The catalysts were prepared by “direct impregnation” of metal sulfate onto the as-synthesized MCM-41 and SBA-15 materials, followed by solid state dispersion and thermal decomposition. Measurements of XRD and nitrogen adsorption isotherms showed that the structures of resultant materials retain well-ordered pores, even with ZrO2 loading as high as 50 wt%. The characterization results indicated that most of the promoted sulfated zirconia were well dispersed on the internal surface of the ordered mesopores. The catalytic behavior of the alumina-promoted sulfated zirconia supported on mesoporous silica was studied in n-butane isomerization. The supports of mesoporous structures led to high dispersion of sulfated zirconia in the meta-stable tetragonal phase, which was the catalytic active phase. The high performance of alumina-promoted catalysts was ascribed to the sulfur retention by alumina.

Mesostructured Sulfated Zirconia with High Catalytic Activity in n-Butane Isomerization

A mesostructured sulfated zirconia with a large surface area (189 m2/g) has been successfully prepared using a triblock copolymer as a structure-directing agent. The resulting material was characterized by XRD, TEM, nitrogen adsorption, FTIR and TG/DTA, which suggested that the mesostructured sulfated zirconia was tetragonal crystalline. Catalytic testing showed that the mesostructured sulfated zirconia was much more active than conventional sulfated zirconia for n-butane isomerization.

Well-dispersed gallium-promoted sulfated zirconia on mesoporous MCM-41 silica

Gallium-promoted sulfated zirconia (SZ) was confined inside pure-silica MCM-41 (abbreviated as SZGa/MCM-41), where the latter served as a host material. It was prepared by direct dispersion of metal sulfate in the as-synthesized MCM-41 materials, followed by thermal decomposition. The SZGa/MCM-41 catalysts were characterized by XRD, N2 adsorption, HRTEM, DRIFT, NH3-TPD, and TPR. The experimental results showed that the ordered porous host structure was still maintained in the catalyst. SZ was in meta-stable tetragonal phase and highly dispersed on the interior surface of MCM-41 even at a high loading of 50 wt%. Additionally, a small fraction of SZ nanoparticles on the external surface of MCM-41 was obtained. The catalytic activity of SZGa/MCM-41 was examined in n-butane isomerization. In comparison to SZ/MCM-41 without promoter, the catalytic activities of the Ga-promoted catalysts were greatly improved. The reason proposed for the higher activity of the Ga-promoted catalysts was that Ga enhances the oxidizing ability of the catalysts.

Ga-promoted tungstated zirconia catalyst for n-butane isomerization

Ga-promoted tungstated zirconia (GWZ) was prepared by a slurry impregnation method. The textural properties as well as the acidities of the Ga-promoted catalysts were characterized by X-ray powder diffraction (XRD), N2 adsorption, NH3 temperature-programmed desorption (NH3 TPD), microcalorimetry and H2 temperature-programmed reduction (H2 TPR). The catalytic behavior of GWZ for n-butane isomerization was studied in the presence of hydrogen. In comparison to tungstated zirconia (WZ), the catalytic activity of the Ga-promoted catalyst was greatly improved. The reason proposed for the higher activity of the Ga-promoted catalysts was that Ga enhances the oxidizing ability of the catalysts.

Isomerization of n-butane by gallium-promoted sulfated zirconia supported on MCM-41

The n-butane isomerization reaction on sulfated zirconia (SZ) supported on MCM-41 mesoporous molecular sieve (SZ/MCM-41) was studied at various reaction temperatures in the presence of hydrogen. The catalytic activity was significantly improved with the addition of an appropriate amount of gallium as a promoter. The best conversion was achieved when the catalyst was promoted by 1.7 wt% gallium and calcined at 680 °C. Although the deactivation of these catalysts in the initial stage was observed the deactivated Ga-promoted SZ/MCM-41 catalysts (SZG/MCM-41) could be completely regenerated in air at 450 °C. The Pt-impregnated SZG/MCM-41 catalyst exhibited higher steady conversion compared with the Pt-free form. These halogen-free catalysts have advantages over other strong acid catalysts, in overcoming corrosion and environmental problems.