Ikusei Nakamura

On the role of gallium for the aromatization of lower paraffins with Ga-promoted ZSM-5 catalysts

Abstract Aromatization of butane or propane was conducted with a series of ZSM-5 catalysts. A small amount of oxygen in the feed promoted butane conversion to aromatic hydrocarbons on H-ZSM-5. It suggests that if hydrogen atoms on the zeolite surface are removed effectively, H-ZSM-5 exhibits a high selectivity for aromatic hydrocarbons. A hybrid catalyst composed of the physical mixture of Ga/SiO 2 and H-ZSM-5 showed comparable activity and aromatic selectivity to those of the Ga-supported ZSM-5 zeolite, whereas the Ga/SiO 2 itself exhibited little catalytic activity for the paraffin conversion and olefin aromatization. The excellent promotional effect of Ga/SiO 2 for aromatics formation was observed only when it was intimately contacted with H-ZSM-5. These results suggest that the supported Ga promotes the zeolite-catalyzed aromatization of lower paraffins by promoting hydrogen desorption via the ‘reverse spillover’ effects.

Development of new disposable catalyst for waste plastics treatment for high quality transportation fuel

Abstract An iron supported coal-derived active carbon catalyst showed excellent activity for liquefaction of polypropylene at low reaction temperature (380°C) to give colorless distillates selectively (98 wt.-%) in the presence of small amount of H2S. Free radical on active carbon should initiate a cracking reaction by hydrogen abstraction to form a hydrocarbon radical. H2S and HS· should promote radical transfer from the hydrocarbon radical to large size hydrocarbon molecule to suppress consecutive cracking of the hydrocarbon radical and to promote cracking of the large size molecule which cannot contact with solid catalyst.

Toluene disproportionation over NiS/SiO2-USY hybrid catalysts: effects of spilt-over hydrogen

Abstract Toluene disproportionation was studied on hybrid catalysts composed of physically mixed NiS/SiO 2 and USY zeolite at 623 K-723 K, 1.0 MPa and W/F = 4.6g h/mol . The activity of the NiS/SiO 2 -USY hybrid catalyst was two times higher than that of USY in hydrogen atmosphere. Also USY hybrid catalysts containing NiS/Al 2 O 3 , NiS/TiO 2 and Mo/S 2 Al 2 O 3 showed high activity for toluene disproportionation. The amount of deposited coke on NiS/SiO 2 , USY zeolite and NiS/SiO 2 -USY (USY content 50%) catalysts was 0.45, 16.1 and 7.6%, respectively, which suggests that coke deposited only on the zeolite. Although the rate of coke deposition was scarcely affected by the presence of NiS/SiO 2 , the deactivation rate was effectively suppressed by the presence of NiS/SiO 2 and gaseous hydrogen. It was suggested that hydrogen species supplied by hydrogen spillover at NiS sites and inter-particle migration promote the turnover frequency of toluene disproportionation at Bronsted acid sites on USY zeolite surface.

Oxidative dehydrogenation of lower paraffins with ZSM-5 zeolite catalysts

Abstract It was found that the oxidative dehydro-aromatization of lower paraffins was effectively catalysed by either a protonic or metal ion-exchanged ZSM-5 zeolite at temperatures from 450 to 550°C. Oxygen reacted selectively with surface hydrogen to promote its removal as water, to decrease its surface concentration, and, thus, to enhance the formation of aromatic hydrocarbons.

m-Xylene transformation over Ni/SAl2O3-USY hybrid catalysts Effects of hydrogen spillover

Abstract m-Xylene transformation (isomerization and aromatics hydrogenation) on Y zeolite (USY) was markedly promoted by the physically mixed sulfided nickel supported on Al2O3 (Ni/SAl2O3) in the presence of hydrogen, while Ni/SAl2O3 showed no activity for these reactions, and coke deposition on USY and m-xylene disproportionation were not affected by Ni/SAl2O3. Also, under nitrogen atmosphere, all reactions were unaffected by Ni/SAl2O3. Studies of H-D exchange of OH groups on USY zeolite with gaseous D2 by FT-IR spectroscopy showed that the ratio of the exchange rate of USY, Al2O3-USY and Ni/SAl2O3-USY catalyst was 3.8, 1 and 14.5, respectively, at 523 K and 62.5 kPa D2. It was concluded that the H-D exchange of OH groups (including Bronsted acid sites) on USY surface in the Ni/SAl2O3-USY catalyst was mainly due to hydrogen spillover through NiS site dissociating gaseous hydrogen, with the spillover hydrogen migrating to the USY surface. This probably promoted m-xylene isomerization and helped maintain a higher activity of hydrogenation for aromatic rings on the zeolite.

Hydrogen spillover on Ni(S)/Al2O3-ultrastable Y zeolite and its effect on xylene isomerization

The catalytic activity of ultrastable Y zeolite (USY) form-xylene isomerization in the presence of hydrogen is markedly promoted by physically mixing with Ni(S)/Al2O3 under the conditions of 603 K and 1.0 MPa. The study on H-D exchange of the OH groups on the USY zeolite surface showed that the exchange rate in Ni(S)/Al2O3-USY was five times higher than that of USY alone. It was considered that active hydrogen species, formed on Ni(S) sites and spilled over to Al2O3 and then to USY, promote the acid catalysis on the USY.

Acidic functions of spilt-over hydrogen

In many acid catalyzed reactions are involved metal-supported solid acids and pressurized hydrogen. Hydrogen gas is not only essential for suppressing the coke formation on catalysts but also promotes acid catalyzed reactions. Authors discuss, in the present paper, reactions of spilt-over hydrogen with the adsorbed species on solid acids and acidic functions of spilt-over hydrogen.

Transfer-hydrocracking of vacuum residue

Abstract Hydrocracking of Arabian Heavy vacuum residue conducted in the presence of metal supported active carbon catalyst gave large amount of distillates (70%) with small hydrogen consumption. Especially, the Yalloum coal derived active carbon catalyst showed high cracking activity. The yield of asphaltene in the product oil was very low, whereas the coke yield was relatively high. In the metal-free active carbon system, the coke yield and the content of olefins, sulfur compounds and asphaltene in the product oil were higher than those of the metal-supported active carbon system. These results suggest that asphaltene in feed oil was adsorbed on the metal supported active carbon catalyst and was decomposed or dehydrogenated on it to form coke and hydrogen atoms. The hydrogen atoms formed migrated on the carbon surface to reach the metal site and transferred to free radicals, olefins or organo sulfur compounds.

Low temperature hydrocracking of paraffinic hydrocarbons over hybrid catalysts

A hybrid catalyst, which was prepared by physical mixing of a H-ZSM-5 and Pd/SiO2, showed an excellent activity for the hydrocracking of n-paraffins at low reaction temperature (503 K). In the n-heptane cracking, the hybrid catalyst gave only isomerized heptane and propane and equimolar amount of i-butane whereas the products on H-ZSM-5 alone distributed from C3 to C9 and C4 products contained all kind of paraffins and olefins. The wide product distribution for H-ZSM-5 system should be attributed to the reaction path comprising oligomerization and cracking of the oligomer. The simple products for the H2-hybrid system should be formed through no other reaction path than the primary cracking reaction on H-ZSM-5, which proceeds through a intermediate containing the protonate dialkylcyclopropane structure.

Hydrocracking of residual oils with iron supported zeolite containing catalyst

Abstract Hydrogen spillover on a hydrocracking catalyst containing an iron supported Y zeolite has been studied. An iron supported Y zeolite was prepared by treating NH 4 -Y zeolite with aqueous solution of ferric nitrate. The iron supported zeolite showed high toluene dispropor-tionation activity in the presence of hydrogen and hydrogen sulfide, while it was poisoned by potassium ion exchange. A hybrid catalyst prepared by physically mixing a USY and the poisoned iron supported zeolite showed the high disproportionation activity, while the USY and the poisoned iron supported zeolite showed low activity. It was suggested that spillover hydrogen is supplied from iron species to Bronsted acid sites on zeolites to promote acid catalyzed reaction. In the case of hydrocracking catalyst composed of transition metals, iron supported zeolite and alumina, spillover hydrogen is also supplied from transition metals on alumina to zeolite surface to promote acid catalyzed reaction.