The catalytic activity of immobilized on modified silica metalloporphyrins bearing antioxidative 2,6-di-tert-butylphenol pendants

A comparative study of the catalytic activity of supported manganese(III) and iron(III) chlorides of meso-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin (R₄PMnCl, R₄PFeCl) and meso-tetraphenylporphyrin (TPPMnCl, TPPFeCl) is reported. The metalloporphyrins have been immobilized via coordination bond on the surface of two series of imidazole modified silica, imidazole propyl silica (IPS) and imidazole 3-(glycidyloxypropyl) silica (IGOPS). The heterogenised catalysts have been evaluated for hydrocarbon oxidation by sodium periodate. The critical role of 2,6-di-tert-butylphenol groups on the periphery of porphyrin ring in their catalytic activity has been evaluated and pertinent structural and mechanistic aspects are discussed.     

H3PW12O40 Supported on AlMCM-41 molecular sieves: An effectual catalyst for t-butylation of anisole

Mesoporous AlMCM-41 (Si/Al = 25) molecular sieves was synthesized and impregnated with different loadings (10, 20 and 30 wt% H₃PW₁₂O₄₀) of phosphotungstic acid. Their catalytic performance was examined in the vapour phase alkylation of anisole with tert-butanol. The major products were found to be 2-tert-butyl anisole (2-TBA), 4-tert-butyl anisole (4-TBA), 2,4-di-tert-butyl anisole (2,4-DTBA). 4-TBA was the major product formed with high selectivity. The influence of temperature, feed ratio, WHSV was studied and the results are discussed.     

Oxidative dehydrogenation of n-butane over mesoporous VO x /SBA-15 catalysts

Mesoporous VO _x /SBA-15 catalysts with different V contents were evaluated for the oxidative dehydrogenation of n-butane and characterized by N₂ adsorption, XRD, HRTEM, H₂-TPR, NH₃-TPD, XPS, and EPR techniques. Compared to conventional V₂O₅/SiO₂ catalysts, the VO _x /SBA-15 catalysts showed better performance. The good performance can be attributed to the good dispersion of V species, presence of V⁴⁺ species and the pore structure.     

Ni–Pt/H-Y Zeolite Catalysts for Hydroisomerization of n-Hexane and n-Heptane

Ni–Pt/H-Y zeolite catalysts with different Ni contents were prepared and applied to the hydroisomerization of n-hexane and n-heptane in the temperature range 225-375 °C. ESCA studies show the complete reduction of Ni species up to 0.3 wt% Ni addition over 0.1 wt% Pt/H-Y and further addition leads to the occurrence of unreduced nickel species as NiAl₂O₄. A TEM study shows the formation of bimetallic (Ni–Pt) particles of nanoscale size and the average particle size is found to increase with increasing Ni loading. Acidity measurements by NH₃-TPD and pyridine-adsorbed FTIR spectroscopy show the increasing occupation of acid sites by the added nickel when increasing the nickel loading. The catalytic activity of Ni–Pt/H-Y zeolite and Pt/H-Y catalysts was compared and it was found that addition of Ni up to 0.3 wt% increases the n-hexane and n-heptane conversion, multibranched isomer selectivity and sustainability of the catalysts due to better metal-acid synergism, complete reduction of Ni species and the formation of catalytically active Ni–Pt bimetallic particles. Further Ni addition leads to a decrease in conversion and multibranched isomer selectivity and an increase in the cracked products, which may be due to the presence of unreduced Ni species and pore blockage by larger-sized bimetallic particles formed.     

Catalytic property of Pt/AlSBA-15 in selective catalytic reduction of NO

Pt-supported on mesoporous SBA-15 catalysts (Pt/SBA-15) have been investigated for selective catalytic reduction of NO by propene in excess oxygen. Catalytic activity of Pt/SBA-15 can be improved by the post-synthesis modification of Al into SBA-15. The resulting material (AlSBA-15) retains a hexagonal order and physical properties of the parent SBA-15 and shows new acid sites. Increased acid sites are confirmed by NH₃-TPD. Medium acid site appeared at 200 °C and broad strong acid site appeared above 250 °C. A certain degree of support acidity of Pt/AlSBA-15 increased the NO conversion, but when there are too many acid sites, carbon deposition becomes extensive and lead to decrease the NO conversion. The influence of different Pt loadings on the catalytic properties was also investigated.     

Tetralin oxidation over chromium-containing molecular sieve catalysts

A series of catalysts in which a transition metal (Fe, Co, and Cr) is incorporated into MCM-41, hexagonal mesoporous aluminophosphate (HMA), and AlPO₄-5 matrix was prepared and tested for liquid phase oxidation of tetralin using tert-butyl hydroperoxide as an oxidizing agent. In general, chromium-containing catalysts showed higher catalytic activity as well as higher α-tetralone selectivity than iron or cobalt-incorporated catalysts. In addition, HMA proved more effective as a support material than MCM-41. CrHMA was the most active (64.9% conversion) and selective (80% α-tetralone selectivity) catalyst, but developed metal leaching due to its amorphous pore walls. CrAlPO₄-5, having a crystalline structure, showed higher resistance to metal leaching than CrHMA.     

Partial oxidation of methane over VOx/α-Al2O3 catalysts

The catalytic behavior of a series of VO_x/α-Al₂O₃ catalysts for the partial oxidation of methane has been evaluated. Samples with different vanadia loading were prepared from NH₄VO₃ and V(AcAc)₃. Characterization performed by TPR and oxygen uptake measurements indicates that different VO_x species are present on the samples. The catalytic patterns indicate that each V-surface species possesses different activity and selectivity. Isolated vanadates are the most active and selective towards HCHO, while V₂O₅ crystallites are detrimental to the catalytic performance.     

Ga-Promoted Tungstated Zirconia Catalyst for n-Butane Isomerization

Ga-promoted tungstated zirconia (GWZ) was prepared by a slurry impregnation method. The textural properties as well as the acidities of the Ga-promoted catalysts were characterized by X-ray powder diffraction (XRD), N₂ adsorption, NH₃ temperature-programmed desorption (NH₃ TPD), microcalorimetry and H₂ temperature-programmed reduction (H₂ TPR). The catalytic behavior of GWZ for n-butane isomerization was studied in the presence of hydrogen. In comparison to tungstated zirconia (WZ), the catalytic activity of the Ga-promoted catalyst was greatly improved. The reason proposed for the higher activity of the Ga-promoted catalysts was that Ga enhances the oxidizing ability of the catalysts.     

Facile tailoring of hierarchical mesoporous AlSBA-15 by ionic liquid and their applications in heterogeneous catalysis

Significant enhancement in the performance of incorporation of high content of aluminum within hierarchical mesoporous SBA-15 has been achieved by direct route using urea tetrachloroaluminate ionic liquid as novel aluminum source. The fabricated materials were fully characterized by N₂ sorption isotherms, powder X-ray diffraction (XRD), FT-IR, ²⁷Al MAS NMR, XRF, HRTEM and FESEM. The acidic properties of these materials have been examined using NH₃-TPD. The catalytic performance was investigated using cumene cracking and the esterification reaction as a probe molecules to estimate the acidity of the material. It is worth noting that the ionic liquid with accomplished Al–O–Si bonds is an efficient precursor to synthesis AlSBA-15 with high aluminum content (nSi/mAl?=?7) without destroying the structural order of the material in acidic medium. ²⁷Al MAS NMR spectra of AlSBA-15 show that all aluminum species were incorporated into the SBA-15 framework with nSi/mAl ratio up to 7. Overall, this work emphasize that the AlSBA-15 materials contain Bronsted and Lewis acid sites with medium acidity which makes them adequate to be adopted as acid catalysts in heterogeneous catalysis.     

Preparation of ZnFe2O4 Catalysts by a Co-precipitation Method Using Aqueous Buffer Solution and Their Catalytic Activity for Oxidative Dehydrogenation of n-Butene to 1,3-Butadiene

Zinc ferrite (ZnFe₂O₄) catalysts were prepared by a co-precipitation method using aqueous buffer solution with different pH (pH = 6−12), and applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene. Conversion of n-butene and yield for 1,3-butadiene showed volcano-shaped curves with respect to pH value employed during the co-precipitation step. NH₃-TPD experiments were conducted to correlate the acid property with the catalytic performance of zinc ferrite catalysts. It was revealed that the catalytic performance of zinc ferrite catalysts in the oxidative dehydrogenation of n-butene was closely related to the surface acidity of the catalysts. Conversion of n-butene and yield for 1,3-butadiene increased with increasing surface acidity of the catalysts. Among the catalysts tested, the zinc ferrite catalyst prepared at pH = 8 showed the best catalytic performance in the oxidative dehydrogenation of n-butene, which was attributed to its largest surface acidity.     

CpMo(CO)3Cl as a precatalyst for the epoxidation of olefins

The tricarbonyl complex CpMo(CO)₃C1 was found to act as a precatalyst for the reaction of tert-butyl hydroperoxide and olefins to yield the corresponding epoxides and diols. Under the reaction conditions, oxidative decarbonylation leads to the formation of the dioxo complex CpMoO₂Cl. The catalytic recyclability and the effect of temperature on the catalytic results have been examined, and a reaction mechanism proposed, supported by kinetic modelling.     

Alkylation of Hydroquinone with tert-Butanol Catalyzed by Polymer-supported Sulfonimide

Polystyrene with pendant perfluorobutylsulfonylimide (PPFSI) was developed as a novel polymer-supported strong acid catalyst for alkylation of hydroquinone (HQ) with tert-butanol (TBA), and highly selective synthesis of 2-tert-butyl hydroquinone (2-TBHQ) was investigated over PPFSI under various experiment conditions. When the molar ratio of TBA to HQ was 1.2:1, using 3 mol% of PPFSI as catalyst in 1,2-dichloroethane at 130 °C for 5 h, the maximum of selectivity (85.9%) of 2-TBHQ was obtained while the conversion of HQ was 76.7%. Compared with other solid acid catalysts PPFSI was found to be a very effective and reusable catalyst for alkylation of hydroquinone with tert-butanol.     

Preparation,characterization and testing of Cr/AlSBA-15 ethylene polymerization catalysts

Ethylene polymerization catalysts have been prepared by grafting chromium(III) acetylacetonate onto AlSBA-15 (Si/Al = ∞, 156, 86 and 30) mesoporous materials. A combination of XRD, nitrogen adsorption, TEM, ICP-atomic emission spectroscopy, H₂-TPR, TGA, UV–vis and FT-IR spectroscopy, were used to characterize the prepared Cr–AlSBA-15 catalysts. By reducing the Si/Al ratio of the AlSBA-15 supports increases the amount of chromium anchored, promotes the stabilization of chromium species as chromate and decreases the reduction temperature of Cr⁶⁺ ions determined by H₂-TPR. Attachment of Cr species onto AlSBA-15 surface results from the interaction of hydroxyl groups with the acetylacetonate ligands through H-bonds. On the contrary, a ligand exchange reaction may occur over siliceous SBA-15.The polymerization activity of Cr–AlSBA-15 catalysts is significantly improved by increasing aluminium content of the AlSBA-15 supports. Particularly, the chromium catalyst prepared with AlSBA-15 (Si/Al = 30) support is almost four times more active than a conventional Cr/SiO₂ Phillips catalyst. Polymers obtained with all the catalysts showed melting temperatures, bulk densities and high load melt indexes indicating the formation of linear high-density polyethylene.     

Mesoporous molecular sieves: alkylation of anisole using tert-butylalcohol

Mesoporous aluninosilicate Al-MCM-41 molecular sieves with Si/Al ratios 25, 50, 75 and 100 have been synthesized under hydrothermal condition and these materials were characterized by XRD, FTIR, BET and pyridine adsorption techniques. The catalytic performance was examined in the vapor phase tert-butylation of anisole with tert-butanol at the temperatures between 150 and 250 °C under atmospheric pressure. The results indicate that Al-MCM-41 (25) was found to be more active than its relatives. The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4-DTBA). Maximum conversion of anisole is observed at 175 °C and decreased thereafter with increasing temperature. The influence of molar feed ratio, influence of temperature, WHSV and time on stream on the selectivity of products was investigated and the results are discussed.     

Propane oxidative dehydrogenation over vanadia catalysts supported on mesoporous silicas with varying pore structure and size

The structural characteristics and the performance of vanadia catalysts (0.7–8 wt.% V) supported on mesoporous (MCM-41, HMS, MCF, SBA-15), microporous (silicalite) and non-porous (SiO₂) silicas in oxidative dehydrogenation of propane were investigated. The structure of vanadia species, the redox and the acidic properties of the catalysts were studied using in situ Raman spectroscopy, TPD- NH₃ and H₂-TPR. The only vanadia species detected on the surface of HMS and MCM-41 for V loadings up to 8 wt.% were isolated monovanadates indicating high vanadia dispersion. Additional bands ascribed to V₂O₅ nanoparticles were evidenced in the case of SBA-15 and MCF supported catalysts while these bands were the only ones identified on the surface of the catalysts supported on silicalite and non-porous silica. The catalysts supported on mesoporous HMS and MCM-41 materials showed the best performance achieving high propane conversions (35–40%) with relatively high propene selectivities (35–47%). Lower activity due to the lower degree of vanadia dispersion, caused by the partial destruction of the pore structure was observed for the SBA-15 and MCF supported catalysts. The degree of dispersion of the V species on the catalyst surface and not the pore size and structure of the mesoporous support or the acidity/reducibility characteristics mainly determine the catalytic activity towards propene production. In addition, it was shown that the pore structure and size of the mesoporous supports did not have any significant effect in the turnover rates (TOF values) of propane conversion (and propene formation at low propane conversion, below ca. 10%). However, the highest propene yield (up to 19%) and stable catalytic behavior was attained for catalysts supported on HMS mesoporous silica, and especially for those combining framework mesoporosity and textural porosity (voids between primary nanoparticles).     

Tert-Butylation of Biphenyl over Mordenites

H-mordenites are very highly shape-selective catalysts in the alkylation of biphenyl with tert-butanol under liquid phase conditions using n-decane as a solvent with a selectivity to 4-(tert-butyl)biphenyl above 98% and to 4,4-di(tert-butyl)biphenyl near 100% to give 24% yield of 4,4-di(tert-butyl)biphenyl using H-MOR(45).     

Nitrous Oxide Reduction with Ammonia and Methane Over Mesoporous Silica Materials Modified with Transition Metal Oxides

Transition metal oxides (Cu, Cr and Fe) were deposited on various mesoporous silicas (MCM-48, SBA-15, MCF and x-MSU) by an impregnation method. Electron microprobe analysis, BET, UV-VIS-DRS and temperature programmed desorption of NH₃ were used for the characterization of the samples. The modified mesoporous silicas were tested as catalysts of the N₂O decomposition and the N₂O reduction using ammonia and methane. The Cu-containing samples presented the highest catalytic activity in the N₂O decomposition, while the Cr- and Fe-modified materials were more active in the reduction of nitrous oxide with NH₃ and CH₄. The type of the silica support strongly influenced the catalytic performance of the studied materials.     

A comparative study of the selective oxidation of NH3 to N2 over gold, silver and copper catalysts and the effect of addition of Li2O and CeOx

This paper describes the selective oxidation of ammonia into nitrogen over copper, silver and gold catalysts between room temperature and 400 °C using different NH₃/O₂ ratios. The effect of addition of CeO_x and Li₂O on the activity and selectivity is also discussed. The results show that copper and silver are very active and selective toward N₂. However the multicomponent catalysts: M/Li₂O/CeO_x/Al₂O₃ (M: Au, Ag, Cu) perform the best. On all three metal containing catalysts the activity and selectivity is influenced by the particle size and the interaction between metal particles and support.     

Novel MnO x Catalysts for NO Reduction at Low Temperature with Ammonia

Novel MnO_x catalysts for NO reduction at low temperature with NH₃ have been prepared by a simple precipitation method using sodium carbonate. The catalysts thus obtained have exhibited excellent catalytic activity in the temperature range of 348–473 K compared with other MnO_x-based catalysts, which is probably due to its high surface area as well as framework structure and composition. The high catalytic activity is maintained in the presence of 20 vol% water vapor in the feed.     

Performance of Pt/MgAPO-11 Catalysts in the Hydroisomerization of n-dodecane

MgAPO-11 molecular sieves with varying Mg contents synthesized by the hydrothermal method were used as supports for bifunctional Pt/MgAPO-11 catalysts. MgAPO-11 molecular sieves and the corresponding catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), temperature-programmed desorption of NH₃ (NH₃-TPD), differential thermogravimetric (DTG) analysis, temperature-programmed reduction of H₂ (H₂-TPR), H₂ chemisorption and catalytic reaction evaluation. The results indicated that the acidity generated via the substitution of Mg²⁺ for Al³⁺ in the framework increased with the Mg content. Acting as acidic components, the MgAPO-11 molecular sieves loaded with Pt were tested in the hydroisomerization of n-dodecane. Optimum isomer yield was obtained over the Pt/MgAPO-11 catalyst that had neither the highest acidity nor the highest Pt loading among the tested catalysts. In fact, the activity and the isomer yield both could attain a maximum on 0.5 wt.% Pt/MgAPO-11 catalysts with differing Mg contents. A lower Mg content resulted in an insufficient acidity, whilst a higher Mg content weakened the dehydrogenation/hydrogenation function of the Pt. These inappropriate balances between the acidic and the metallic functions of the catalysts would lead to low activities and isomer yields. On the other hand, the 0.5 wt.% Pt/MgAPO-11(3) catalyst was found to have a good balance between the acidic and the metallic functions, and thus exhibited both high activity and isomer yield in comparison with the conventional 0.5 wt.% Pt/SAPO-11 catalyst.