Tian-Sheng Zhao

Effects of zinc on Fe-based catalysts during the synthesis of light olefins from the Fischer-Tropsch process

Abstract Fe-based catalysts for the production of light olefins via the Fischer-Tropsch synthesis were modified by adding a Zn promoter using both microwave-hydrothermal and impregnation methods. The physicochemical properties of the resulting catalysts were determined by scanning electron microscopy, the Brunauer-Emmett-Teller method, X-ray diffraction, H 2 temperature-programed reduction and X-ray photoelectron spectroscopy. The results demonstrate that the addition of a Zn promoter improves both the light olefin selectivity over the catalyst and the catalyst stability. The catalysts prepared via the impregnation method, which contain greater quantities of surface ZnO, exhibit severe carbon deposition following activity trials. In contrast, those materials synthesized using the microwave-hydrothermal approach show improved dispersion of Zn and Fe phases and decreased carbon deposition, and so exhibit better CO conversion and stability.

Ordered mesoporous alumina-supported bimetallic Pd–Ni catalysts for methane dry reforming reaction

To compare the influence of Pd addition to Ni supported on ordered mesoporous alumina catalyst, prepared highly ordered mesoporous alumina (MA) was used as catalyst support for methane dry reforming under atmospheric pressure. Ni and Pd were impregnated on this support to obtain both monometallic and/or bimetallic catalysts, respectively. The fresh and spent catalysts were characterized by N2 physical adsorption, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), laser Raman spectroscopy and temperature-programmed hydrogenation (TPH). The XRD and HRTEM analysis results showed that Ni–Pd nanoalloy was formed after H2 reduction. The catalytic performance analysis results indicated that the bimetallic nanoalloy catalysts showed higher activity than the monometallic catalyst. The deposition of carbon during the reaction was analyzed. The results indicated that different supported metal species led to different carbon species which influenced catalytic performance.

Effect of preparation of Fe–Zr–K catalyst on the product distribution of CO2 hydrogenation

The precursors of Fe–Zr–K catalysts were prepared by microwave assisted homogeneous precipitation followed by incipient wetness impregnation. The obtained mesoporous particles were small and uniformly shaped. After reduction, the catalyst showed high activity for the selective production of light olefins from CO2 hydrogenation, superior to the catalyst obtained by co-precipitation. Characterization indicated that with Zr addition, the reducibility, surface basicity and surface atomic composition of the samples varied with the Zr content. The CO2 adsorption ability of the samples was increased and the samples became hard to reduce as a result of the interaction between iron species and zirconia. In the case of using 5Fe–1Zr–K under selected conditions of 1000 h−1, 320 °C and 2 MPa, the CO2 conversion and the selectivity of C2–C4 olefins reached 54.36% and 53.63%. The olefin/paraffin ratio in the C2–C4 hydrocarbon product fraction reached 6.44. The selectivity of CO and C5+ hydrocarbons were 3% and 19.78%, respectively. The catalytic activity remained stable up to 92 h in time-on-stream reaction.

Hydrothermal preparation of Fe–Zr catalysts for the direct conversion of syngas to light olefins

Fe/Zr precursors were prepared by a one-step and two-step hydrothermal process respectively, following K promotion by incipient wetness impregnation, which then were used for the selective production of C2–C4 olefins via Fischer–Tropsch synthesis from syngas. The textural properties, phase structure, reduction behavior and the catalytic performance of the obtained catalyst samples were greatly affected by different preparation procedures. The T–Fe/Zr samples prepared by the two-step hydrothermal process caused a decrease in the surface area and easier reduction of iron species compared with that of the O–Fe/Zr samples prepared by the one-step hydrothermal process. The T–Fe/Zr samples before and after K promotion showed preferred orientation along the (−111) and (111) lattice planes of ZrO2 in contrast to the ZrO2 (101) lattice plane on O–Fe/Zr samples. For CO hydrogenation, all the catalysts exhibited high activity and good stability. The T–Fe/Zr–K catalysts with highly dispersed zirconia on the iron surface could prevent Fe–Zr mixed oxide formation by decreasing the interaction between iron and zirconia, leading to a slight increase in C2–C4 olefin selectivity and improvement on the product distribution.

Preparation of layered K/Mg-Fe-Al catalysts and its catalytic performances in CO hydrogenation

Abstract A series of K promoted K/MgFeAl-HTLcs catalysts with different Mg/Fe/Al molar ratios were prepared by means of coprecipitation and impregnation method for direct synthesis of light olefins from CO hydrogenation. The samples were characterized by XRD, N2 adsorption-desorption, SEM, TG, H2-TPR and XPS measurements. The results show that MgFeAl-HTLcs catalyst precursors have typical layered structure. MgO, Fe2O3 and small amount of MgFeAlO4 are formed after calcination. MgCO3 and Fe3O4 could be observed after reaction, and a little Fe5C2 iron carbide with broad and weak peaks appears simultaneously. Thermal stability of K/MgFeAl-HTLcs is improved due to recovery of hydrotalcite-like structure after K promotion. With increase of Al content, specific surface area of the precursors decreases monotonically after structure reconstruction. Reduction of Fe2O3 to Fe3O4 is inhibited with addition of Al, compared with K/Mg-Fe sample. Fe enrichment before reaction and K enrichment after reaction are observed on secondary calcination samples. During CO hydrogenation, the prepared samples show high activity and C2=-C4= selectivity with low C5+ weight fraction. C5+ hydrocarbons decrease and olefin selectivity increases with increasing Fe/Al molar ratio. The C5+ decreases from 22.17% to 10.90%, and C2=-C4= weight content increases from 40.98% to 47.28% on K/1.5Mg-0.67Fe-0.33Al sample compared with that of K/1.5Mg-0.67Fe sample.