Side chain alkylation of 2-picoline with formaldehyde over alkali modified zeolites

The catalytic side-chain alkylation of 2-picoline with formaldehyde (37 wt/v) was studied over alkali and alkaline earth metal ion modified zeolites in vapor phase conditions at atmospheric pressure, and at a reaction temperature of 300°C. A mixture of vinylpyridine and ethylpyridine were formed by the alkylation of the corresponding picoline over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of side-chain alkylation of 2-picoline was studied over various alkali modified zeolite molecular sieves like ZSM-5 (SiO₂/Al₂O₃ = 30), X, Y, Mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2-picoline when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) and K-Cs-ZSM-5 (30) gave best conversion of 2-picoline and selectivity to vinylpyridine. Cs-ZSM-5 (30) and K-ZSM-5 (30) were employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2-picoline independently. The effects of alkali metal ion content (K, Cs) and precursors of potassium ion on catalytic activity in side-chain alkylation was studied. An attempt has been made to correlate between the basicity with the activity of side-chain alkylation. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed reaction mechanism. The selectivities of 2-vinylpyridine were 81.7, 90.8, and 94.8% at 65.4, 62.1 and 57.2% conversions at 300°C from 2-picoline and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and K-Cs-ZSM-5 (30) respectively. Indian Institute of Chemical technology (IICT) communication no: 020707     

High growth of SWNTs and MWNTs from C2H2 decomposition over Co-Mo/MgO catalysts

A series of MgO supported catalysts having Co and Mo metals 5-40 wt.% in a ratio of 1:1 was prepared by impregnation method. Carbon nanotubes (CNTs) were grown over the catalysts by decomposition of C₂H₂ at 800 °C for 30 min. It was found that 5 and 10 wt.% Co-Mo/MgO catalysts produced single-wall nanotubes (SWNTs), whereas 20, 30 and 40 wt.% Co-Mo/MgO catalysts produced multi-wall nanotubes (MWNTs). The catalyst Mo/MgO was inactive in growing CNTs. In Co-Mo/MgO catalysts, however Mo generated a favorable environment to grow SWNTs. The growth of SWNTs was strongly dependent on the formation of small clusters of cobalt, which may generate from the decomposition of CoMoO₄ species during the nanotube growth. MWNTs were produced over comparatively larger cobalt clusters generated from Co₃O₄ phase during the nanotube growth stage. The yields of SWNTs were about 6% and 27% over 5 and 10 wt.% Co-Mo/MgO catalysts, respectively. MWNTs yield (576%) was observed over 40 wt.% Co-Mo/MgO catalyst. Carbon yield (%) highly varied with acetylene concentration.     

The effect of P/Ta ratio on sorbitol dehydration over modified tantalum oxide by phosphoric acid

A series of modified hydrated tantalum oxides (Ta₂O₅·nH₂O) with various contents of phosphoric acid were prepared and firstly used as the catalysts for sorbitol dehydration to isosorbide. The catalytic performance of Ta₂O₅ was improved significantly after modification, and the isosorbide selectivity over 0.8P/TaO was improved from 3.8 to 48.3% with nearly 100% sorbitol conversion. Characterization with NH₃-TPD, FT-IR, Raman and XRD demonstrated that the introduction of phosphate has transformed Ta₂O₅ into two kinds of new crystalline phases exhibiting various surface acidities. The P-OH species in TaH(PO₄)₂ were mainly responsible for the promotion of catalytic performance over modified oxides.     

One-step synthesis of methyl isobutyl ketone from acetone and hydrogen over Pd/(Nb2O5/SiO2) catalysts

The surface-phase oxides of niobia on silica substrate ((Nb₂O₅/SiO₂), NS(x)) were prepared and characterized. Such oxides were used as supports for palladium catalysts. The one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen in liquid phase was also investigated over Pd/NS(x) catalysts. Experimental results indicate that these catalysts were effective for the formation of MIBK; since little of the parallel by-product of isopropanol (IPA) was formed, these catalysts reached selectivities of 88–92% MIBK and 2–3% IPA at 30–35% conversion. The reactivity of Pd/NS(x) declined obviously with an increase of water content that accumulated in a semi-batch reaction system. The water could be partially expelled and the deactivation of catalysts could be improved by using a fixed bed continuous flow reaction system.     

Characterization and catalytic application of MnCl2 modified HZSM-5 zeolites in synthesis of aromatics from syngas via dimethyl ether

The conversion of syngas to aromatics via dimethyl ether was investigated over MnCl₂ modified HZSM-5 zeolites. The results demonstrated that 2%MnCl₂ modified HZSM-5 (SiO₂/Al₂O₃ = 38) exhibited higher p-xylene selectivity than other catalysts and further decreased 1,2,4,5-tetramethylbenzene selectivity. The CO conversion was obviously increased after 5%MnCl₂ modification to HZSM-5. The catalysts were characterized by XRD, BET, XPS, FT-IR, NH₃-TPD, SEM, element analysis and O₂-TPO. The loading amount of MnCl₂ affected the adsorption and reaction of DME molecules on zeolites. Appropriate amount of MnCl₂ introduction could adjust the acidity and pore volume of HZSM-5 to increase p-xylene selectivity and CO conversion.     

Catalytic dehydration of methanol to dimethyl ether over modified γ-Al2O3 catalyst

A γ-Al₂O₃ catalyst was modified with metal oxide (Nb₂O₅) in order to improve its activity and stability for dimethyl ether (DME) synthesis from methanol. A series of modified γ-Al₂O₃ catalysts were prepared with Nb₂O₅ and characterized by X-ray diffraction and temperature programmed desorption of ammonia. Results showed that the γ-Al₂O₃ catalyst containing 10 wt.% of Nb₂O₅ exhibited the highest surface area among the modified ones. The number of acid sites of the modified catalysts was increased by the Nb₂O₅ modification. In the chemical reaction of DME synthesis, it was found that the Nb₂O₅ modified γ-Al₂O₃ catalyst exhibited a higher activity in the low temperature region (240 °C-260 °C) and a higher activity than did the untreated γ-Al₂O₃ catalyst.     

Glycerol steam reforming over Ni/γ-Al2O3 catalysts modified by metal oxides

The metal oxides modified Ni/γ-Al₂O₃ catalysts for glycerol steam reforming were prepared by impregnation. Characterization results of fresh catalysts indicated that the molybdates modification abated the acidity and the stronger metal-support interaction of Ni/γ-Al₂O₃ catalysts, leading to a stable catalytic activity. Especially, NiMoLa-CaMg/γ-Al₂O₃ (NiMoLa/CMA) catalyst exhibited no deactivation along with glycerol complete conversion to stable gaseous products containing 69% H₂, 20% CO and 10% CO₂ during time-on-stream of 42 h. TPO of spent Ni/γ-Al₂O₃ catalysts modified by different components showed that the carbon deposit on acidic sites and NiAl₂O₄ species led to catalysts deactivation. A lower reforming temperature and a higher LHSV and glycerol content were helpful to the production of syngas from GSR over NiMoLa/CMA; the reverse conditions would improve the formation of H₂.     

Enantioselective Hydrogenation of N‐Acetyldehydroamino Acids over Supported Palladium Catalysts

The enantioselective hydrogenation of two N‐acetyldehydroamino acids over Cinchona alkaloid‐modified, supported palladium catalysts has been studied. Moderate enantioselectivities, up to 36 %, were obtained in the hydrogenation of 2‐acetamidocinnamic acid over cinchonidine‐modified Pd/TiO₂ under low hydrogen pressure. Increase in the pressure or use of benzylamine as additive led to a gradual decrease in the enantiomeric excess and eventually inversion of the sense of the enantioselectivity. On the contrary, the optical purity of the product resulting from the hydrogenation of 2‐acetamidoacrylic acid was significantly increased by addition of benzylamine to the reaction mixture. Enantiomeric excess values up to 58 % and 60 % were obtained over Pd/Al₂O₃ modified by cinchonidine and cinchonine, respectively. These optical purities are the best obtained in the hydrogenation of dehydroamino acid derivatives over chirally modified heterogeneous metal catalysts.     

Effect of hydrothermal treatment temperature on FCC gasoline upgrading properties of the modified nanoscale ZSM-5 catalyst

Nanoscale HZSM-5 zeolite was hydrothermally treated with ammonia water at different temperatures and then loaded with La₂O₃ and ZnO. The parent and the modified nanoscale HZSM-5 catalysts were characterized by SEM, NH₃-TPD, IR and XRF. The performance of the modified HZSM-5 catalysts for FCC gasoline upgrading was evaluated in a fixed bed reactor in the presence of hydrogen. The results indicated that the modified catalyst which was hydrothermally treated at 400 °C exhibited excellent aromatization activity, isomerization activity and higher ability of reducing olefin content in FCC gasoline. Under the given reaction conditions, the olefin content in FCC gasoline could be decreased from 49.6 to 8.1 vol.%. The catalytic performance of the modified nanoscale ZSM-5 catalyst hardly changed within 300 h time on stream, and the research octane number (RON) of gasoline was preserved.     

Modified Beta Zeolite as Catalyst for Fries Rearrangement Reaction

Modified beta zeolites were applied as catalysts for the Fries rearrangement reaction. The properties of the modified zeolites were characterized by NH₃-TPD, n-hexane and 1,2,4-trimethylbenzene adsorption. Modification with SiO₂ did not block the pores of the beta zeolite but reduced the number of acid sites on the surface. However, when the beta zeolite was modified with Ce₂O₃, the number of acid sites determined by NH₃-TPD increased, which indicated that new acid sites are created by the interaction of cerium oxide and zeolite. Modified beta zeolites and H-beta were applied as catalysts for the Fries rearrangement of phenol acetate. Reaction over H-beta has low selectivity and the catalyst is easily deactivated. SiO₂ modification of the catalyst increases the selectivity of the reaction but decreases the conversion. Ce₂O₃-modified beta zeolites show higher catalytic activity and rearrangement selectivity in the reaction than other catalysts. The stability of the catalyst is also improved after Ce₂O₃ modification. About 70% selectivity and 60-80% conversion can be achieved over 16 wt% Ce₂O₃-modified beta zeolite.     

Catalytic Combustion of Benzene over Au Supported on Ceria and Vanadia Promoted Ceria

Complete oxidation of benzene over Au/CeO₂ and Au/V₂O₅/CeO₂ catalysts were studied. Gold was supported on CeO₂ from different sources by deposition precipitation method. The catalysts were characterized by XRD, BET, X-ray photoelectron spectroscopy, TEM, and H₂-TPR techniques. The catalytic activity toward the complete oxidation of benzene to CO₂ and water were strongly dependent on the kind of CeO₂ sources, loading amount of gold, modified amount of vanadia, and calcination temperature. High activities were obtained on 1% Au/CeO₂ and 2% vanadia modified Au/CeO₂ catalysts calcined at 300 °C. The nanometer size of Au particle and interaction between Au, V₂O₅, and CeO₂ play important roles in determining the activity of benzene complete oxidation.     

Naphthalene oxidation over vanadium-modified Pt catalysts supported on γ-Al2O3

Alumina-supported platinum catalysts modified by vanadium were synthesised and tested for the complete oxidation of naphthalene. The catalysts were characterised by BET, pulsed CO chemisorption, powder X-ray diffraction, laser Raman spectroscopy and temperature-programmed reduction. Whilst BET and CO chemisorption results showed that the addition of vanadium modified both the textural properties of the support and the distribution of Pt, XRD and TPR data suggested the presence of V₂O₅ on catalysts with higher V loadings. TPR data showed that the concentration of V₂O₅ and possibly some other vanadium species increased as the V loading increased. Only 0.5%V was found to promote the activity of the 0.5%Pt/γ-Al₂O₃ catalyst. The activity enhancement has been related to the presence of a more easily reducible vanadium species coupled with the enhanced number of surface Pt sites. On the other hand, the reduced activity demonstrated by catalysts with higher vanadium content (1 – 12%) has been attributed to the presence of crystalline V₂O₅.     

Effect of Pt on stability of nano-scale ZSM-5 catalyst for toluene alkylation with methanol into p-xylene

Shape-selective methylation of toluene (T) with methanol (M) was carried out in continuous flow fixed-bed reactor over Pt-modified nano-scale HZSM-5 catalysts, and excellent stability was obtained. Even after 500 h on stream, toluene conversion of 22.0–23.0% was achieved simultaneously with the para-selectivity of >98%. The presence of Pt on the modified nano-scale HZSM-5 solves the apparent paradox of high para-selectivity and low stability. Catalysts were characterized by using X-ray diffraction (XRD), temperature programmed desorption of ammonia (NH₃-TPD), Pyridine IR (Py-IR), TG-SDTA, scanning electron microscope (SEM), etc. The results show that significant enhancement in stability over Pt-modified nano-scale HZSM-5 catalysts is mainly due to good hydrogenation properties of Pt particles.     

Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with copper, cobalt and calcium

Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped Ni/CeO₂–ZrO₂ catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H₂ chemisorption. For Cu and Co doped catalyst, CuO and Co₃O₄ phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly and the main products were H₂, CO, CH₄ and CO₂. However, the Co doped catalysts showed poor activity and a relatively large amount of C₂H₄, C₂H₆, CH₃CHO and CH₃COCH₃ were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts, CH₃CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO₂ and H₂ were increased and the selectivity to CH₃CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation. For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C.     

Phenylhydrazine rearrangement revisited over modified ZSM-5 catalysts

The rearrangement of phenylhydrazine too- andp-phenylenediamines was carried out over ZSM-5 and its modified catalysts. Sm and V showed the promoting effect. In presence of ammonia flow Ga and Cr modified ZSM-5 catalysts gave good yields ofo- andp-phenylenediamines. The better temperature and WHSV for this reaction are found to be 400°C and 0.25 h^–1 respectively. The SiO₂/Al₂O₃ catalyst showed very low ortho-para selectivity when compared with zeolite catalysts.IICT Communication No. 3372.     

The oxidation activity and acid-base properties of SnO2-based binary catalysts: II. The SnO2MoO3 and SnO2P2O5 systems

The vapor-phase oxidation of 1-butene, butadiene, and acetic acid, the isomerization of 1-butene, and the dehydration and dehydrogenation of isopropyl alcohol (IPA) were carried out, in the presence of an excess of air, over two series of catalysts, SnO₂MoO₃, and SnO₂P₂O₅, and the relationship between the catalytic behavior and the acid-base properties of the catalysts was investigated. The acidity and the basicity of the SnO₂MoO₃ catalysts were measured by studying the adsorption of basic and acidic molecules, respectively, in the gas phase, using both the static and pulse methods. The acidities of the SnO₂MoO₃ catalysts are dramatically high at the Mo content of 30–60 atom%, though those of the SnO₂-rich (Mo < 20 atom%) and MoO₃-rich (Mo > 80 atom%) catalysts are fairly low. The basicity is remarkably enhanced by the introduction of a small amount of MoO₃ (Mo < 5 atom%). It can be said that the catalysts are basic in the MoO₃-poor composition. In the case of the SnO₂P₂O₅ catalysts, the acidity and basicity were evaluated from the catalytic activity for the dehydration of IPA to propylene and the (dehydrogenation rate for IPA)/(dehydration rate for IPA) ratio, respectively. The introduction of P₂O₅ increases the acidity and decreases the basicity, to a very small extent, so it cannot cause a remarkable modification in the catalytic behavior; that is, the SnO₂P₂O₅ catalysts are rather basic.     

CH3-modified Co/Ru/SiO2 catalysts and the performances for Fischer–Tropsch synthesis

CH₃-modified Co/Ru/SiO₂ catalysts were prepared and the catalytic performances for Fischer–Tropsch synthesis were investigated. The modified and unmodified catalysts were characterized by FT-IR, N₂ physisorption, TG, XRD, TPR and DRIFTS. FT-IR indicated an effective surface organic modification. TG suggested that modified catalysts had good thermal stability. XRD and TPR showed that modified catalysts had similar reducibility and Co₃O₄ particle size with unmodified catalyst. During reaction tests in a fixed bed reactor it was found that compared with unmodified Co/Ru/SiO₂ catalyst CH₃-modified Co/Ru/SiO₂ catalysts showed higher selectivity to C₅–C₁₁ hydrocarbons, which should be ascribed to hydrophobic surface of CH₃-modified Co/Ru/SiO₂ catalysts.     

Formylation with supercritical carbon dioxide over Ru/Al2O3 modified by phosphines: heterogeneous or homogeneous catalysis?

The formylation of 3-methoxypropylamine with hydrogen and “supercritical” carbon dioxide over Ru-based catalysts was studied. In this solventless process, carbon dioxide acts as both reactant and solvent. Interestingly, Ru/Al₂O₃ modified by the phosphine 1,2-bis(diphenylphosphino)ethane (dppe) showed a high formylation activity at 100% selectivity, comparable to those of the homogeneous catalysts RuCl₂(dppe)₂ and RuCl₂(PPh₃)₃. Analysis of the reaction mixture by ICP-OES and structural studies by in situ X-ray absorption spectroscopy discovered that the presence of the phosphine modifier led to the formation of a homogeneous ruthenium catalyst.     

Synthesis and physicochemical characterization of nanostructured Pd/ceria‐clinoptilolite catalyst used for p‐xylene abatement from waste gas streams at low temperature

BACKGROUND: The effect of Pd loading, xylene concentration and GHSV on xylene oxidation was tested over Pd/CeO₂(30%)‐clinoptilolite nanocatalysts at low temperatures. The catalysts were prepared by acid treatment of clinoptilolite, followed by the incipient wetness method of synthesized ceria and modified clinoptilolite in PdCl₂ solution. The synthesized nanocatalysts were characterized by XRD, FESEM, EDAX, TEM, BET, FTIR and TG‐DTG analysis. RESULTS: The XRD patterns confirmed the formation of crystalline ceria with an average crystallite size of 11.8 nm. FESEM images showed nanostructures in cavities of natural zeolite, brought about by ceria incorporation and acid activation. TEM analysis showed high dispersion of Pd with a size distribution between 6.6 and 36.7 nm. The quantitative analysis showed that the specific surface area of Pd(1%)/CeO₂(30%)‐clinoptilolite was 77 m² g^?1. The results showed that Pd(1%)/CeO₂(30%)‐clinoptilolite is the most appropriate catalyst, with the conversion more than 90% at 275 °C. CONCLUSIONS: Experimental results established effective performance and durability for the catalysts. As a result, clinoptilolite modification and ceria incorporation significantly altered the samples' morphology at nanoscale, improving the structure of composites and distribution of noble metals. A reaction path was suggested based on the adsorption‐migration of species to reveal the mechanism of p‐xylene oxidation over nanocatalysts. © 2012 Society of Chemical Industry     

H3PW12O40/SiO2 for sorbitol dehydration to isosorbide: High efficient and reusable solid acid catalyst

Tungstophosphoric acids (PW) supported on various metal oxides (SiO₂, γ-Al₂O₃, TiO₂, ZrO₂ and CeO₂) were synthesized and used as catalysts for sorbitol dehydration to isosorbide for the first time. 30% PW/SiO₂ exhibited the best catalytic performance for sorbitol dehydration, over which 56% isosorbide selectivity could be gained at a 95% sorbitol conversion at 250 °C. The catalytic performance of regenerated 30% PW/SiO₂ catalysts by dichloromethane elution showed no loss after recycling five runs. Characterizations with UV-Vis, XRD, NH₃-TPD and thermal analysis techniques revealed that PW had a good dispersion, and the primary Keggin structure was preserved after supporting PW on different supports. The interaction between PW and oxides resulted in different acidity of catalysts, which affected conversion of sorbitol and selectivity for isosorbide. The final acidity order of supported PW catalysts was the following: SiO₂>γ-Al₂O₃>TiO₂ ≈ ZrO₂>CeO₂.