Eika W. Qian

Elucidation of promotion effect of cobalt and nickel on Mo/TiO2 catalyst using a 35S tracer method

Abstract A series of CoMo and NiMo catalysts supported on TiO 2 with various Co/Mo and Ni/Mo molar ratios were prepared to investigate the relationship between the nature of the support and the promotion effect of Co and Ni. The catalytic activities of these catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) were measured. The HDS activity of CoMo/TiO 2 catalysts increased linearly with the addition of cobalt up to Co/Mo ratio of 0.6 and then decreased slightly above this value. Similarly, the HDS activity of NiMo/TiO 2 catalysts increased linearly with the addition of nickel up to Ni/Mo ratio of 0.6 and remained almost constant above this value. The sulfur mobility on the CoMo/TiO 2 and NiMo/TiO 2 catalysts under the reaction conditions was elucidated by a 35 S radioisotope tracer method using 35 S -labeled DBT. The amount of labile sulfur ( S 0 ) increased linearly with the addition of cobalt or nickel up to molar ratio of 0.6. In contrast, no significant difference in the rate constants of H 2 S release ( k RE ) was observed between Co- or Ni-promoted catalysts and non-promoted Mo catalysts at a given temperature. Therefore, the increase in catalytic activity with the addition of cobalt or nickel can be attributed to an increase in the number of active sites.

Elucidation of sulfidation state and hydrodesulfurization mechanism on ruthenium–cesium sulfide catalysts using 35S radioisotope tracer methods

Abstract Alumina-supported ruthenium–cesium catalysts were presulfided using [ 35 S]H 2 S pulse tracer method to evaluate their sulfidation state. Subsequently, using these previously 35 S-labeled catalysts, HDS reactions of dibenzothiophene (DBT) were performed and the mobility of 35 S introduced during the presulfidation stage was investigated. The results showed that the amount of labile sulfur ( S 0 ) was much smaller than the total amount of sulfur accommodated on the catalyst (S total ). DBT conversion and S total increased linearly with Ru content. In a second part, labile sulfur amount was also determined under the catalyst working conditions and different results were obtained. Indeed, when the catalysts were marked with [ 35 S] and with [ 35 S]DBT under HDS reaction conditions, the obtained labile sulfur quantities (S 0A ) were significantly higher than the ones measured during the presulfidation stage ( S 0 ). These results showed that the labile sulfur is not formed on RuCs catalysts until the HDS reaction proceeds, which is quite different from that reported before for Mo, Pt, or Pd systems.

Elucidation by computer simulations of the CUS regeneration mechanism during HDS over MoS2 in combination with 35S experiments

The first part of this paper is a short review of the 35S radioactive tracer methods developed in recent years. Then, the experimental results obtained so far on Mo/Al2O3 catalysts are compared with computer simulation results recently claimed in order to elucidate the coordinatively unsaturated site (CUS) creation/replenishment/ regeneration mechanism over MoS2 crystallites. The computer simulations allowed us to pre-select thermodynamically acceptable mechanisms among a set of suggested ones. Then, by comparison of the calculated activation energies with the 35S experiments results we could further validate the most probable mechanism. This mechanism involved the dissociative adsorption of an H2 molecule on the metallic edge of a MoS2 crystallite surface with further creation of a CUS by release of one H2S molecule in the gas phase. Both laboratory and computer simulated experiments permitted to calculate the activation energy for the H2S liberation reaction. In both cases, this energy was about 10- 12 kcal/mol, confirming the accuracy of the proposed mechanism. Moreover, the calculated activation energy of the rate-limiting step for the creation of one CUS by the proposed mechanism was about 23 kcal/mol, which was also in good agreement with the experimental activation energy of the dibenzothiophene (DBT) hydrodesulphurisation (HDS) reaction (typically about 20- 22 kcal/mol). This correlation indicated that the DBT HDS reaction rate might be intrinsically governed by the CUS formation/replenishment process, i.e. that the vacancy formation process is a crucial parameter in the global HDS reaction mechanism. Nevertheless, in the case of the 4,6-dimethyl DBT (4,6-DMDBT) HDS reaction, the experimental activation energy is higher (approx. 30 kcal/mol), confirming that external parameters induced by the 4,6-DMDBT-specific properties themselves are likely to play an important role in the reaction process, in addition to the ones intrinsic to the catalytic phase.

Hydrodenitrogenation of porphyrin on Ni-Mo based catalysts

Abstract The hydrodenitrogenation (HDN) of porphyrins was carried out over a series of phosphorus containing NiMo/Al2O3 catalysts using a fixed-bed flow reaction system. A method of quantitative analysis of the porphyrin and its derivatives produced by HDN was established. In HDN of porphyrin, four types of hydrocarbons: C8 alkanes, C8 alkenes, C9 alkanes, and C10 alkanes, and two groups of nitrogen-containing compounds: alkyl substituted bipyrrolidines (alkylbipyrrolidines) and alkyl substituted tripyrrolidines (alkyltripyrrolidines) were identified. The hydrogenolysis of porphyrins occurred rapidly at lower temperature but higher temperatures were required for the HDN of porphyrins. The NiMoP3 catalyst showed the highest catalytic activity for the HDN of porphyrins. Based on the characterization of the supports and catalysts, it is suggested that the dispersion of Mo is improved and the number of weak acidic sites on the NiMoP catalysts increases with the addition of phosphorus.

Characterization of sulfur exchange reaction between polysulfides and elemental sulfur using a 35S radioisotope tracer method

A sulfur exchange reaction between di-tert-butylpolysulfides and elemental sulfur was examined using a 35S tracer method and the reaction mechanism was discussed.

Hydrodesulfurization, Hydrodenitrogenation and Hydrodearomatization over CoMo/SAPO-11-Al 2 O 3 Catalysts

The fluidized catalytic cracking (FCC) process is a method for the catalytic conversion of heavy oil into lighter products, and is very important in the petroleum refinery. The main product of the FCC process is FCC gasoline and the by-product is light cycle oil (LCO), which mainly consists of bicyclic or polycyclic aromatic compounds and small amounts of sulfur and nitrogen compounds. Conversion of large content of polyaromatic compounds in LCO to mono-aromatic compounds would yield high added value products for p roduc ing Benzene-Toluene-Xylene (BTXs) . However, conventional hydrotreating catalysts, as well as catalysts for the removal of sulfur compounds and nitrogen compounds cause the hydrogenation of polyaromatic compounds, so no mono-aromatic compounds are obtained. Therefore, a specific catalyst is needed for desulfurization and denitrogenation, and selective hydrogenation of bicyclic or tricyclic aromatic compounds to monocyclic aromatic compounds1). Several models for the structure of the active phase2)~4) of cobalt promoted MoS2 catalysts have been proposed, but the CoMoS phase consisting of cobalt atoms on the edge of MoS2 slabs is widely accepted5)~7). The RimEdge model with two types of active sites, the Rim site and the Edge site, can explain the differences in the hydrogenation (HYD) and hydrodesulfurization (HDS) active sites8). The Rim sites are located only on the top and bottom of the MoS2 slabs, and have both hydrogenation and desulfurization activities. In contrast, the Edge site located on the edge of each layer of the slabs only has desulfurization activity. Based on this model, a catalyst for selective hydrogenation, i.e. higher HDS and/or hydrodenitrogenation (HDN) but lower hydrodearomatization (HDA), could be developed by controlling the proportions of the Rim and Edge sites. The acidity of the support is expected to affect the hydrogenation activity9),10). Higher support acidity enhanced hydrogenation activity of catalyst9). Low acidity zeolite materials such as the SAPO series or SBA series could be used mixed with Al2O3 to decrease support acidity and control hydrogenation catalytic activity. Evaluation of various zeolite types and alumina for hydrocracking catalysts concluded that zeolite with both small crystal size and mesoporous alumina 301 Journal of the Japan Petroleum Institute, 60, (6), 301-310 (2017)

Synthesis of polysulfides using diisobutylene, sulfur, and hydrogen sulfide over solid base catalysts

A series of solid base catalysts were prepared with several alkali and alkaline earth metal species. The catalysts were used in one-stage synthesis processes of polysulfides using diisobutylene (DIB), sulfur, and hydrogen sulfide (H 2S). The possibility of using solid base catalyst as an alternative for a liquid amine catalyst and the effects of preparation conditions on the catalytic activity were discussed. Alumina-supported potassium catalysts showed a catalytic activity comparable to that of dicyclohexylamine. The alkali metal catalysts proved to be more effective than alkaline earth metal catalysts. Further, a three-stage mechanism for polysulfide synthesis using the system of diisobutylene, sulfur, and hydrogen sulfide in the presence of solid base catalysts was suggested. Moreover, a novel [ 14 C]CO2 radioisotope pulse tracer method was developed to determine the amount of CO2 adsorption on solid base catalysts at the temperatures between 100–400 ◦ C and under 0.6–3.1 MPa. The relationship between the uptake amount of CO2 on the alkali metal catalysts and the catalytic activity in syntheses of polysulfides was discussed.

62 Elucidation of behavior of hydrogen on solid catalysts using a tritium tracer method

Hydrogen exchange reaction between tritiated gaseous hydrogen with hydrogen on several catalysts were carried out using a fixed bed pulse flow reactor at 100–600°C and under 1.57 MPa. The amounts of hydrogen uptake onto the catalysts were determined from the radioactivity balance of tritium between input and output. It was found that the hydrogen exchange reaction occurred over γ-Al2O3, K/Al2O3. HY, and NaY but no hydrogen exchange was observed over SiO2 and sulfated zirconia as well as quartz sand. Further, the process of hydrogen exchange was elucidated by analyzing in the wave shape of tritium pulse.