Jie Ren

Conversion of methane and carbon dioxide into synthesis gas over alumina-supported nickel catalysts. Effect of Ni-Al2O3 interactions

A series of alumina-supported nickel catalysts were prepared by calcination of the catalyst precursors in air at different temperatures. The increase in the intensity of Ni-Al2O3 interactions with the calcination temperature was found to be unfavourable to the reduction of the catalyst, and thus caused a decrease in activity for the low temperature reaction between methane and carbon dioxide. However, the catalyst with strong Ni-Al2O3 interactions suppressed carbon deposition effectively, which can be attributed to the formation of spinel, NiAl2O4, after calcination. When the reaction was carried out at 1023 K, all the catalysts tended to exhibit the same activity. At the same time, only filamentous carbon with a hollow inner channel was observed and there were nickel particles on the tip of this filamentous carbon.

Chemical treatment of γ-Al2O3 and its influence on the properties of Co-based catalysts for Fischer–Tropsch synthesis

Abstract Alumina has been pretreated in the presence of medium and then used to prepare the supported Co catalysts. These modified supports and the respective catalysts have been thoroughly characterized by means of methods such as BET, pore size distribution, X-ray diffraction (XRD), ammonia temperature-programmed desorption (NH 3 -TPD), pyridine infrared spectroscopy (Py-FTIR), KBr-IR spectroscopy (FTIR), temperature-programmed reduction (TPR), oxygen titration, hydrogen chemisorption, in situ diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) and CO hydrogenation to understand how chemically-treated alumina influences the properties of Co catalysts. These characterizations clearly show the changes of morphology (surface area, pore volume, pore size distribution and crystallite phase) as well as chemical properties (e.g. acidity) of the supports. Although the cobalt oxide crystallite sizes of the oxidic catalyst precursor are almost unaffected by different support pre-treatment, the reducibility of these catalysts vary greatly. And the support pre-treatment remarkably influences the adsorption and catalytic properties of these Co catalysts. The acetic acid-treated support has a negative effect on the catalytic properties of Co catalyst, whereas the ammonia and ammonium nitrate-treated samples show pronounced effects on the catalytic behaviors of Co catalysts.

Support effect of Co/Al2O3 catalysts for Fischer–Tropsch synthesis☆

Abstract Cobalt supported on different γ-alumina carries prepared by incipient wetness impregnation are used to investigate the effect of support on the performance of cobalt catalysts for Fischer–Tropsch synthesis (FTS). It is found that the acidity of support has a great influence on the interaction between metallic cobalt and support and then the reducibility of cobalt. The support with low acidity leads to the higher active FTS catalysts. Furthermore, the high reducibility and more bridged type CO which is favored by γ-alumina with low acidity appears to be responsible for high C 5 + hydrocarbon selectivity and low methane selectivity.

n-Dodecane Hydroconversion over Ni/AlMCM-41 Catalysts

Mesoporous aluminosilicate (AlMCM-41) samples were synthesized using various aluminum sources: Al(NO3)3, aluminum isoproxide (Al(OPri)3) and NaAlO2. It was found that the AlMCM-41 prepared using NaAlO2 contained more framework Al(IV) species and stronger acidity compared with those from Al(NO3)3 and Al(OPri)3, respectively. Supported with 2.0 wt% nickel metal, the Lewis acid sites of the AlMCM-41 samples increased due to the compensating effect of the coordinately unsaturated nickel cations, while the Bronsted acid sites slightly decreased because of the coverage of the nickel species. In the n-dodecane hydroconversion, the Ni-containing AlMCM-41 sample prepared by using NaAlO2 gave the symmetrical carbon number distribution and the largest amount of C4–C9 hydrocarbons in the cracked products due to its proper balance between metal and acid functions.

Rare earth-modified bifunctional Ni/HY catalysts

Abstract Rare earth elements (La, Nd, Sm, Gd and Dy) were characterized by NH 3 -TPD, Py-FTIR and CO-DRIFTS and tested for n -octane hydroconversion. The Bronsted acidity of modified catalysts increased as the rare earth ionic radius became longer. A similar relationship between metallic function and ionic radius was also observed. Among rare earth elements, lanthanum improved the nickel dispersion and then the ratio of metallic to acid functions. This led to the high catalytic activity and isomerization selectivity of Ni/HY catalyst. However, the catalysts modified by the other rare earth elements showed poor catalytic performance due to the reduction of Bronsted acidity and nickel dispersion, especially a lower ratio of metallic to acid functions.

Role of La2O3 in Pd-supported catalysts for methanol decomposition

Systems of Pd supported on various La2O3-modified γ-Al2O3 and CeO2–Al2O3 catalysts were tested for catalytic methanol decomposition and characterized by means of XRD, BET, TPR, H2-chemisorption and CO–FTIR. The addition of lanthanum significantly improved the selectivity of CO and H2 for all the catalysts but showed a different influence on the catalytic activity in two systems. Methanol conversion decreased on La2O3-modified Pd/γ-Al2O3 catalysts, in line with the reduction of Pd dispersion, while the addition of La2O3 improved the dispersion of Pd and reinforced Pd–CeO2 interaction for La2O3-modified Pd/CeO2–Al2O3 catalysts, which resulted in a high production rate of CO and H2. Thus, a synergistic effect between CeO2 and La2O3 was observed on γ-Al2O3-supported Pd catalyst for methanol decomposition.

Catalytic conversion of n-parafins in supercritical phase

Abstract The catalytic conversion of n-paraffins in supercritical phase, including catalytic dehydrogenation of C 10 -C 14 n-paraffins to linear monolefins and Pt reforming of heptane at low temperature, was investigated here. The results indicated that the supercritical catalysis led to the improvement of both conversion of the reactants and selectivity of the main products as well as the reduction of coke formation.

Effects of lanthanum on the properties of bifunctional Ni/HY catalyst

A series of lanthanum modified-Ni/HY bifunctional catalysts for n-octane hydroconversion were prepared by ion-exchange method, and the influence of lanthanum contents on the activity and the selectivity was investigated. Py-FTIR and CO-DRIFTS results indicated that the addition of lanthanum could adjust the acidity and the metal state over Ni/HY catalyst, and consequently change the ratio of metal to acid functions. It was found that the best catalytic performance at the lanthanum exchange of ca. 8 wt.% was due to the suitable metal/acid ratio.