Weihua Qian

Effects of H2S on hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene on alumina-supported NiMo and NiW catalysts

Abstract Effects of the H2S partial pressure on the catalytic activity and product selectivity of the hydrodesulfurization (HDS) reactions of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) were investigated over the sulfided NiMo/Al2O3 and NiW/Al2O3 catalysts under the deep desulfurization conditions (sulfur concentrations

Elucidation of molybdenum-based catalysts using aradioisotope tracer method Part 1.—Hydrodesulfurization activityand structure of sulfided molybdena–aluminacatalysts

Hydrodesulfurization of radioactive 35 S-labelled dibenzothiophene was carried out over a series of sulfided molybdena–alumina catalysts containing 6–20 wt.% molybdena at temperatures in the range 280–380°C and at a pressure of 50 kg cm -2 . The sulfur exchange data and hydrodesulfurization activity were simultaneously obtained and the effect of molybdenum content on the structure of sulfided catalysts was estimated. The sulfur exchange rates were approximately the same for all samples at the same temperature and apparent activation energies of hydrodesulfurization reactions were 20±2 kcal mol -1 for all catalysts. These results suggest that the mechanism of hydrodesulfurization and the nature of active sites did not vary with molybdenum content. On the other hand, the amount of labile sulfur increased linearly with the molybdenum content up to 2.89 atom nm -2 but then levelled off with further loading of molybdenum. Thus, it was suggested that a monolayer dispersion of molybdenum sulfide on alumina was maintained up to 2.89 atom nm -2 but some crystallites of molybdenum sulfide would be formed when molybdenum was added beyond 2.89 atom nm -2 . Moreover, the sulfur exchange rate hardly varied with the molybdenum content and the hydrodesulfurization rates of dibenzothiophene on the catalysts paralleled the amount of labile sulfur.

Hydrodesulfurization and hydrogenation on alumina-supported tungsten and nickel-promoted tungsten catalysts

Hydrodesulfurization (HDS) of radioactive 35S-labeled dibenzothiophene was carried out over a series of alumina-supported W-based catalysts containing ca. 10–35 wt.% WO3 and 0–9 wt.% NiO at temperatures in the range 220–400°C and under a reaction pressure of 50 kg cm-2. The catalytic activities of the catalysts changed depending on the W loadings and sulfidation temperature for W–Al2O3 catalysts. Moreover, the HDS and hydrogenation (HYD) activity of W–Al2O3 catalysts were remarkably enhanced with the addition of nickel. Further, the amount of labile sulfur (S0) on the W–Al2O3 catalyst was much less than that on the corresponding Mo catalyst although the strength of the W–S bond is weaker than that of Mo–S. This is attributed to the fact that the sulfidation of the W–Al2O3 catalyst and the formation of the W–S bond are more difficult. On the other hand, S0 and the rate constant of H2S release (kRE) increased significantly on addition of nickel, as in the case of the Co–Mo catalyst. Moreover, the Ni-promoted W–Al2O3 catalyst with higher Ni/W ratio (0.6) also showed S0 and kRE comparable to those of the corresponding Co–Mo catalyst. These results suggested, therefore, that the promoting effect of nickel enhanced the relative ease of sulfidation of W catalysts and resulting in formation of more active sites simultaneously.

Elucidation of molybdenum-based catalysts using a radioisotope tracer method Part 2 Promotion effect of cobalt on molybdena/alumina catalyst

Hydrodesulfurization (HDS) reactions of radioactive 35S-labelled dibenzothiophene were carried out over a series of cobalt-promoted molybdena/alumina catalysts at temperatures between 240 and 320°C and under 50 kg cm-2 pressure. HDS and hydrogenation (HYD) activities of Mo/Al2O3 catalysts were remarkably enhanced with the addition of cobalt, the maximum promotional effect occurring with a Co/Mo molar ratio of ca. 0.5. The amount of labile sulfur and the rate constant of sulfur exchange increased significantly with the addition of cobalt, indicating that cobalt makes the sulfur more mobile and that the active phases in the promoted catalysts are different from that in the unpromoted catalyst. The promoting effect of cobalt was thus attributed to the formation of more active sites. On the other hand, the amount of labile sulfur increased linearly with the Co/Mo ratio up to ca. 0.5 whereas the rate constant of sulfur exchange remained almost constant. Moreover, the enhancement in catalytic activity did not change significantly with the cobalt content. The increase in the catalytic activity with the cobalt content was thus ascribed to an increase in the number of the same active sites.

Sulfur exchange on CoMo/Al2O3 hydrodesulfurization catalyst using 35S radioisotope tracer

Abstract A commercial CoMo/Al 2 O 3 catalyst was labeled with the radioisotope 35 S in hydrodesulfurization (HDS) of 35 S-labeled dibenzothiophene ( 35 S-DBT) in a high-pressure flow reactor at 50 kg/cm 2 . Then, HDS of 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) or sulfur exchange of H 2 S were carried out on the labeled catalyst at 50 kg/cm 2 and 260–360°C. The amounts of labile sulfur participating in the reaction were determined from the radioactivity of 35 SH 2 S released from the 35 S-labeled catalyst. In the HDS reactions, the amount of labile sulfur participating in the reaction decreased in the order: DBT > 4-MDBT > 4,6-DMDBT. In the sulfur exchange reaction with H 2 S, the adsorption of H 2 S on the catalyst reached saturation above a H 2 S partial pressure of 0.36 kg/cm 2 . It was suggested that the release of H 2 S from the labile sulfur may be the rate determining step of the HDS reaction.

Elucidation of dimethylsulfone metabolism in rat using a 35S radioisotope tracer method

Abstract The metabolism of dimethylsulfone was quantified for possible medical applications based on the hypothesis that the agent may be metabolized to yield methionine or its metabolites. The 35 S-labeled dimethylsulfone and methionine are orally administrated to rat. Over 80% of the administrated dimethylsulfone is metabolized in the rats tissues, and 59.7–79.1% of it is then excreted into the urine as 35 S-containing metabolites; 3.5–10.3% of the same remains incorporated in the tissues. The uptake of radioactivity, though different from the quantity of methionine in percentage at the retained site, is observed in the blood, spleen and hair, and over 80% of the administered [ 35 S] dimethylsulfone is excreted the same day. Meanwhile, the distribution of the 35 S concentrations of both agents in the rat system suggests that this compound had been metabolized to yield certain sulfur-containing compounds.

Hydrodesulfurization and hydrogenation of radioactive 35S-labeled dibenzothiophene on alumina-supported chromium and promoted chromium catalysts

Hydrodesulfurization (HDS) reactions of radioactive 35S-labeled dibenzothiophene ([35S]DBT) were carried out over a variety of Cr/Al2O3 with 5.5–33.3 wt.% CrO3 and over promoted Me-Cr/Al2O3 (Me/Cr = 0.4, 0.6; Me = Ni, Co and Cu) catalysts at temperatures in the range of 300–380°C and under a reaction pressure of 5.0 MPa. The HDS activity of Cr/Al2O3 catalysts increased with increasing Cr loadings to 33.3 wt.% CrO3. Moreover, both HDS and hydrogenation (HYD) activities of Cr/Al2O3 catalysts were enhanced with the addition of Ni and Co. In contrast, adding Cu to Cr/Al2O3 catalyst decreased its catalytic activity inversely. Further, the results obtained from the HDS reaction of 35S-labeled dibenzothiophene indicated that the amount of labile sulfur increased on adding Ni and Co to Cr/Al2O3 catalysts whereas it decreased on adding Cu. It is suggested, therefore, that the addition of Ni and Co weakens the strength of the chromium–sulfur bond on the sulfided Cr/Al2O3 catalyst, and brings about increases in amount of labile sulfur and in catalytic activity of the Cr catalyst.

Sulfidation of nickel- and cobalt-promoted molybdenum–alumina catalysts using a radioisotope 35S-labeled H2S pulse tracer method

Abstract The sulfidation state in a series of nickel- and cobalt-promoted Mo/Al 2 O 3 catalysts was investigated using 35 S radioisotope pulse tracer methods (RPTM). Several pulses of 35 S -labeled H 2 S ([ 35 S ]H 2 S) were introduced into catalysts in a nitrogen stream until the radioactivity in the recovered pulse approached the radioactivity of the introduced pulse. From the amount of [ 35 S ]H 2 S introduced, the amount of sulfur accumulated on the catalyst was estimated. The amounts of sulfur accumulated on the catalysts increased with increasing temperature for all catalysts and the cobalt-promoted catalysts showed features similar to those of the nickel-promoted catalysts. It was found that the sulfided states of the catalysts close to the stoichiometric states, where Ni, Co and Mo are present as NiS, Co 9 S 8 and MoS 2 , was attained at 400°C for all catalysts. Moreover, it was suggested that only molybdenum was sulfided below 300°C; the sulfidation of nickel oxide and cobalt oxide in the Ni– or the Co–Mo/Al 2 O 3 catalyst is more difficult at lower temperatures and the sulfidation of nickel and cobalt species occurs only at higher temperatures (above 300°C).

Sulfidation state of alumina-supported molybdenum catalysts estimated by a 35Sradioisotope tracer method

The sulfidation state in Mo/Al2O3 and Co-Mo/Al2O3 catalysts have been investigated using a 35S pulse tracer method. [35S]H2S pulses were introduced into Mo/Al2O3 or Co-Mo/Al2O3 in a nitrogen stream until the amount of radioactivity in one pulse was constant, i.e. the catalyst no longer reacted with [35S]H2S. From the amount of reacted [35S]H2S, the amount of sulfur accumulated on the catalyst was estimated. The amounts of sulfur accumulated on the Mo/Al2O3 and Co-Mo/Al2O3 catalysts increased with increasing temperature. The amounts of sulfur accumulated on Mo/Al2O3 with 12 wt.% MoO3 at 100, 200, 300 and 400°C were 34.0, 38.5, 50.7 and 60.5 mg S (g cat)-1, respectively and the value at 400°C corresponded to a sulfidation state of MoS2.2/Al2O3. At the same temperature, the amount of sulfur accumulated on Mo/Al2O3 increased with increasing the amount of molybdenum loaded. Below 300°C, the amount of sulfur accumulated on Mo/Al2O3 was almost same as that on CoMo/Al2O3. The amount of sulfur accumulated on CoMo/Al2O3 (CoO: 3.8 wt.%, MoO3: 12.3 wt.%) at 400°C was 73.4 mgS (g cat)-1, larger than that on Mo/Al2O3 with 12 wt.% MoO3. These results suggest that only molybdenum is sulfided in both Mo/Al2O3 and CoMo/Al2O3 catalysts below 300°C and that only at 400°C is cobalt on CoMo/Al2O3 sulfided.

Elucidation of hydrogen mobility in coal using a tritium pulse tracer method. Hydrogen exchange reaction of coal with tritiated gaseous hydrogen

Abstract The hydrogen exchange of coal with gaseous hydrogen was carried out between 200 and 300°C using a pulse flow reaction system in the absence and presence of a Pt/Al 2 O 3 catalyst to estimate the mobility of hydrogen in coals. In the absence of the catalyst, hydrogen exchange hardly occurred and hydrogen exchange ratio (HER) was fewer than 1% in most of coals used. Hydrogen exchange reaction between coal and gaseous hydrogen was enhanced remarkably in the presence of Pt/Al 2 O 3 catalyst and HER was increased with temperature. The hydrogen mobility in coal was lower for higher rank of coals at each temperature. Further, the amount of hydrogen in functional groups of coal, which is contributed to the hydrogen exchange with tritiated gaseous hydrogen, could be estimated by the treatment of the tritiated coals with water. It was suggested that almost all hydrogen of functional group in coals were exchanged with gaseous hydrogen at high temperatures over 250°C in the presence of the catalyst.