Liquidphase tert-butylation of cresols catalysed by 12-tungstophosphoricacid and 12-tungstosilicicacid supported onto neutral alumina

A comparative study on tert-butylation of cresols such as o-cresol, m-cresol and p-cresol with tert-butyl alcohol was carried out over 30% 12-tungstophosphoricacid and 12-tungstosilicicacid supported onto neutral alumina in liquid phase under mild conditions. The catalysts show high activity in terms of % conversion and % selectivity for the products, p-tert butyl o-cresol, o-tert butyl m-cresol, o-tert butyl p-cresol, under mild conditions.     

Esterification of stearic acid with p-cresol over modified Indian bentonite clay catalysts

The esterification of stearic acid with p-cresol using modified Indian bentonite clay catalysts has been reported. The reaction was studied over exchanged clays, acid activated clays, exchanged acid activated clays, aluminium pillared clay, aluminium pillared acid activated clay, molecular sieve Al-MCM-41, zeolite Hβ, ZrO₂, S-ZrO₂, p-TSA, montmorillonite K10, and montmorillonite KSF in o-xylene for 6 h. The catalysts were characterized by X-ray diffraction and surface area measurements. The acidity was determined by n-butylamine back-titration method and DRIFTS after pyridine adsorption. Acid activated Indian bentonite (AAIB) was found to be a better catalyst compared to other catalysts in the esterification of stearic acid with p-cresol.     

Effects of preparation methods of support on the properties of nickel catalyst for hydrogenation of m-dinitrobenzene

Using tetraethyl orthosilicate (TEOS) as the precursor of silica, the silica aerogel and xerogel, which were used as supports of nickel-based catalysts for liquid hydrogenation of m-dinitrobenzene to m-phenylenediamine, were prepared by the sol-gel method combined with supercritical drying (SCD) and conventional drying, respectively. Then, a series of nickel-based catalyst samples supported on these supports were prepared by the incipient wetness impregnation method with an aqueous solution of nickel nitrate as well as lanthanum nitrate as impregnation liquids. Based on the characterization results of nitrogen adsorption-desorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature-programmed desorption of hydrogen (H₂-TPD), and catalytic activity evaluation, the physico-chemical properties and catalytic performances of the catalysts were investigated. The results show that the nickel crystallites on the binary nickel catalyst using silica aerogel as support are of smaller particle size. However, compared with the sample supported on silica xerogel, the nickel catalyst supported on the silica aerogel exhibits lower activity and selectivity for the hydrogenation of m-dinitrobenzene because it has a lesser amount of active sites and weaker absorption ability to reactants caused by sintering of the nickel crystallites. The addition of promoter La₂O₃ could increase the activity and selectivity of the catalysts. Among all the nickel-based catalyst samples prepared, the La₂O₃ promoted ternary nickel-based catalyst supported on silica xerogel exhibits the highest activity and selectivity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine, which could be attributed to its highest active surface area and appropriate absorption strength to reactants. Over this promising catalyst, the conversion of m-dinitrobenzene and the yield of m-phenylenediamine could reach 97.0% and 93.1%, respectively, under proper reaction conditions of hydrogen pressure 2.6 MPa, temperature 373 K, and reaction time 1 h. Translated from Journal of Chemical Engineering of Chinese Universities, 2006, 20(5): 723–727 [译自: 高校化学工程学报]     

Statistical optimization of process variables in batch alkylation of p-cresol with tert-butyl alcohol using ionic liquid catalyst by response surface methodology

Alkylation of p-cresol with tert-butyl alcohol was studied using ionic liquid catalyst prepared from N-(1,4-sulfonic acid) butyl triethylammonium hydrogen sulfate. An experimental design using response surface methodology (RSM) is used to optimize the process parameters in this batch alkylation to minimize rigorous experimental procedures and conserve the catalyst. The parameters, namely, temperature, reactant mole ratio, catalyst (IL) to p-cresol mole ratio and time of reaction on the conversion of p-cresol and yield of 2-tert-butyl-p-cresol (TBC) were optimized using Box–Behnken design. Low temperature, low p-cresol to alcohol ratio and low catalyst (IL) to p-cresol ratio in a batch reactor were found to maximize conversion of p-cresol and yield of TBC.     

The Di-t-butylation of p-cresol with t-butanol in Supercritical CO2 over Tungstophosphoric Acid Supported on Ordered Mesoporous Silica

Tungstophosphoric acid (HPW) supported on MCM-41 was an excellent catalyst for the t-butylation of p-cresol to 2,6-di-t-butyl-4-methylphenol (2,6-DTBPC) in supercritical CO₂; however, zeolites, H-Y and H-Beta, only gave 2-t-butyl-4-methylphenol (2-TBPC) because of their limitation in pore size. The yield of 2,6-DTBPC was maximized at 110 °C, and further increase in temperature rather decreased the yield. The yield of 2,6-DTBPC was maximized at 10–11 MPa CO₂ pressure, and further increase of the pressure decreased in the conversion of phenol and the yield of 2,4-DTBC. The thermogravimetric analysis of used catalysts showed that the coke-formation was minimized in supercritical CO₂ compared to the other reaction media such as in liquid phase and in N₂ atmosphere.     

Ultra-rapid synthesis of syngas by the catalytic reforming of methane enhanced byin-situ heat supply through combustion

Development in highly active catalysts for the reforming of methane with CO₂ and partial oxidation of methane was conducted to produce hydrogen and carbon monoxide with high reaction rates. An Ni-based four-components catalyst, Ni-Ce₂O₃-Pt-Rh, supported on an alumina wash-coated ceramic fiber in a plate shape was suitable for the objective reaction. By combining the catalytic combustion of ethane or propane, methane conversion was markedly enhanced, and a high space-time yield of syngas, 25,000 mol/l·h was obtained at a catalyst temperature of 700 ‡C or furnace temperature of 500 ‡C. The extraordinary high space-time yield of syngas was also confirmed even under the very rapid flow rate conditions as a contact time of 3 m-sec by using a monolithic shape of catalyst bed without back pressure.     

Spinel-Type Cobalt Chromites as Novel and Highly Ortho-selective Catalysts for Phenol Alkylation

The gas phase catalytic alkylation of phenol with methanol was investigated over a series of spinel-type cobalt chromite catalysts. The molar ratio of Co/Cr and the calcination temperature have considerable effect on the catalytic performance of the samples. Among them, the Co/Cr=0.8 sample calcined at 723 K shows the highest activity (97.3% phenol conversion) with a total 94.8% ortho-selectivity to o-cresol and 2,6-xylenol at the reaction temperature of 693 K.     

A new catalytic transesterification for the synthesis of N, N-dimethylaminoethyl acrylate with organotin catalyst

A new transesterification method for preparing N, N-dimethylaminoethyl acrylate (DMAEA) from methyl acrylate (MA) and dimethylaminoethanol (DMAE) was carried out in the presence of organotin catalyst. Among the catalysts examined, (C₈H₁₇)₂Sn(OCOC₁₁H₂₃)₂(TD) is the most active one for the reaction. The products were characterized by gas chromatography, IR spectroscopy, NMR spectroscopy and Mass spectroscopy. The effects of various reaction conditions such as the different catalysts, the reactants ratio, the amount of catalyst, the reaction time on the DMAE conversion, the selectivity to DMAEA and the DMAEA yield were investigated. Experimental results indicated that the sort of catalyst is vital to improving DMAEA yield. The reactants ratio could effect on the DMAE conversion, the selectivity to DMAEA and the DMAEA yield. The 96.28% conversion of DMAE was obtained over catalyst TD, the yield of DMAEA could reach 94.65%, the selectivity is 98.68%. A possible catalytic mechanism of transesterification of DMAE and MA with organotin catalysts was also presumed.     

负载磷钨酸催化剂制备与催化性能

引　言随着环境保护要求的日益严格 ,人们正在加紧开发对环境友好的固体酸催化剂 ,杂多酸作为一类新型的催化材料受到研究者的广泛重视[1～ 4 ] .杂多酸是酸强度较为均一的纯质子酸 ,其酸性不但强于硅酸铝和各种分子筛等固体酸 ,也强于氢氟酸和硫酸等液体酸 .目前杂多酸 (如磷钨酸 )已成功地用于烯烃水合、醇脱水、酯化和烷基化等反应过程 ,取代硫酸等强腐蚀性液体酸催化剂 ,解决了传统工艺所存在的严重污染环境和腐蚀设备问题 ,明显地提高了产品质量和收率[1] .但纯固体杂多酸比表面积很小 (1～ 10ｍ2 ·ｇ- 1) ,因此在实际应用中需要将杂…     

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.     

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.     

Hydroisomerization of Long-Chain Alkane Over Pt/SAPO-11 Catalysts Synthesized from Nonaqueous Media

SAPO-11 molecular sieves were synthesized from nonaqueous media. The effects of Si and Al sources as well as solvents on the catalytic performance of SAPO-11 were investigated by the hydroisomerization reaction of n-dodecane. The samples were characterized by XRD, XRF, N₂-adsorption, SEM, NH₃-TPD, IR-NH₃ and ²⁹Si CP MAS NMR. The SAPO-11 samples synthesized with tetraethoxysilane as the Si source showed higher Si incorporation contents than the SAPO molecular sieves prepared with polymeric Si sources (fumed silica and Si colloidal gel). The reaction results showed that Pt/SAPO-11 catalysts synthesized from ethylene glycol and glycerol media with the monomeric Si and Al sources (tetraethoxysilane, aluminum isopropoxide) exhibited higher catalytic activities than those catalysts with the polymeric Si or Al (pseudo-boehmite) sources, due to the larger external surface area and higher acidity of the former ones. Especially, the catalyst synthesized in an ethylene glycol medium possessed the highest catalytic activity. Over this catalyst, 88% conversion of n-dodecane was achieved at a low temperature of 250 °C.     

In situ 13C MAS NMR Study on the Mechanism of Butane Isomerization Over Catalysts with Different Acid Strength

Reaction mechanism of skeletal isomerization of n-butane over sulfated zirconia (SZ), Cs_2.5H_0.5PW¹²O₄₀ (Cs_2.5) and H-form mordenite (H-MOR) catalysts was studied using ₁₃C MAS NMR with ₁₃C-labeled n-butane. The isomerization of n-butane over SZ type catalysts proceeds predominantly via a monomolecular mechanism below 333 K and gradually changes to a bimolecular alkylation-β-scission mechanism as the reaction temperature is increased to 423 K. Iron promoter in SZ catalyst facilitates the bimolecular process. The n-butane isomerization over Cs_2.5 also proceeds mainly via a monomolecular mechanism below 373 K. The bimolecular mechanism becomes significant as the reaction temperature is increased to 423 K. On both SZ and Cs_2.5 catalysts hydrogen inhibits the isomerization reaction, in particular the bimolecular process. In contrast, the n-butane isomerization over H-MOR with relatively moderate acid strength proceeds mainly via a bimolecular mechanism at 473 K. The kinetics of n-butane isomerization on SZ below 333 K and Cs_2.5 below 373 K are well represented by the Langmuir–Hinshelwood equation for a reversible first order surface reaction, further supporting that a monomolecular mechanism proceeds primarily on SZ and Cs_2.5 catalysts at early reaction stage. All results suggest that the stronger the acidity of the catalyst the lower the reaction temperature of n-butane isomerization and the more contribution of the monomolecular mechanism. The overall mechanism of 1−₁₃C-n-butane reaction on SZ, Cs_2.5 and H-MOR catalysts including ₁₃C scrambling and butane isomerization is proposed.     

Wet oxidation of wastewater containing hydrocarbons by novel supported Pd catalysts

Pd catalysts supported on TiO₂, ZrO₂, ZSM-5, MCM-41 and activated carbon were used in catalytic wet oxidation of hydrocarbons such as phenol, m-cresol and m-xylene. It was found that the Pd/TiO₂ catalyst was highly effective in the wet oxidation of hydrocarbon. The activities of catalysts with various hydrocarbon species, catalyst support, oxidation state of catalyst performed in a 3-phase slurry reactor show that reaction on Pd surface is more favorable than that in aqueous phase and that the active site is oxidized Pd in catalytic wet air oxidation of hydrocarbons. Based on the experimental results, a plausible reaction mechanism of wet oxidation of hydrocarbons catalyzed over Pd/TiO₂ catalyst was proposed. This catalyst is superior to other oxide catalysts because it suppressed the formation of hardly-degradable organic intermediates and polymer.     

Effect of preparation method on the acidities of Al-B-O x mixed oxides

A series of Al-B-O _x metal oxides with various Al/B ratios were prepared with impregnation and coprecipitation methods. The surface acidic properties of these catalysts were examined by temperature-programmed desorption (TPD) of ammonia and the dehydration reaction of isopropanol. The dehydration reaction was carried out in a continuous-flow microreactor at 130–260 °C under atmospheric pressure. The results of TPD of ammonia indicated that the surface acidity of Al-B-O _x material is medium-strong. The acidic strengths are approximately the same for all the Al-B-O _x samples, regardless of its preparation method. In addition, their acid strengths are much stronger than that of pure alumina. However, the acid concentration is increased with decreasing the Al/B atomic ratio of the catalyst. The dehydration activities of these catalysts are increased with decreasing the Al/B atomic ratios of the samples. The results also indicated that the addition of boron on alumina, no matter what preparation method is used, could significantly enhance the acidities of the catalysts. A compensation effect was observed in isopropanol dehydration reaction over these catalysts. The preexponential factor decreases and activation energy increases with increasing Al/B ratio of the catalyst. The results can be interpreted in terms of the acidity of the catalyst.     

Isomerization of n-Heptane over Ni-WO x /SiO2-Al2O3 Catalysts. Effect of Operating Conditions, and Nickel and Tungsten Loading

Isomerization of n-heptane over Ni-WO _x /Al₂O₃-SiO₂ catalysts was carried out in a continuous flow fixed-bed reactor under atmospheric pressure. The first part of this study deals with the preparation of two series of catalysts (A and B) by the sol-gel method, while the second part deals with the isomerization of n-heptane. The principal objective of this study was to choose the catalyst giving the best isomer yield (di- and tri-branched ones) with optimum reaction conditions (reaction temperature, reduction temperature and time on stream). From the results obtained, the optimum nickel content was found to be 15 wt% and it seems that the incorporation of tungsten (B series) leads to a significant enhancement in the activity of the prepared catalysts. After running on stream for 100 min, the catalyst with 15% nickel and 10% tungsten (B4 catalyst) gives the best results (29% conversion and 70% selectivity) at 250 °C.     

Metal cation-exchanged montmorillonite clay as catalysts for hydroxyalkylation reaction

Several solid acid catalysts were prepared by exchanging metal cations such as Zn²⁺, Fe³⁺ and Al³⁺ with montmorillonite clay. Among these, Al-montmorillonite showed the highest acidity determined by the pyridine-IR as well as NH₃-TPD methods. A systematic comparison of the performance of these catalysts along with parent montmorillonite was carried out for the hydroxyalkylation of p-cresol with formaldehyde to give 2, 2′-methylenebis (4-methyl phenol) (DAM). It was found that the activity of these catalysts was in accordance with the increase in acidity of parent montmorillonite after the exchange of cations in the order of Zn²⁺, Fe³⁺ and Al³⁺. The selectivity pattern was also influenced by the exchanged cations. Since Al-montmorillonite showed the highest conversion of 51% with 98% selectivity to DAM, the effects of various reaction parameters, namely, mole ratio, catalyst concentration, temperature, reaction time on conversion and selectivity pattern were also studied using the same catalyst. This catalyst also showed an excellent stability as evidenced by its eight times reuse.     

Development of iso-octane fuel processor system for fuel cell applications

An iso-octane fuel processor system with three different reaction stages, autothermal reforming (ATR) reaction of iso-octane, high temperature shift (HTS) and low temperature shift (LTS) reactions, was developed for applications in a fuel cell system. Catalytic properties of the prepared Ni/Fe/MgO/Al₂O₃ and Pt–Ni/CeO₂ or molybdenum carbide catalysts were compared to those of commercial NiO/CaO/Al₂O₃ and Cu/Zn/Al₂O₃ catalysts for ATR and LTS reaction, respectively. It was found that the prepared catalysts formulations in the fuel processor system were more active than those of the commercial catalysts. As the exit gas of iso-octane ATR over the Ni/Fe/MgO/Al₂O₃ catalyst was passed through Fe₃O₄–Cr₂O₃ catalyst for HTS and Mo₂C or Pt–Ni/CeO₂ catalyst for LTS reaction, the concentration of CO in hydrogen-rich stream was reduced to less than 2400 ppm. The results suggest that the iso-octane fuel processor system with prepared catalysts can be applied to PEMFC system when a preferential partial oxidation reaction is added to KIST iso-octane reformer system.     

Hβ/HZSM-5 Composite Carrier Supported Catalysts for Olefins Reduction of FCC Gasoline Via Hydroisomerization and Aromatization

In order to develop a novel catalyst system that has excellent olefin reduction ability for FCC gasoline without loss in research octane number (RON), different catalysts supported on single- and binary-zeolite carriers consisting of Hβ or/and HZSM-5 were prepared and their catalytic performances for FCC gasoline upgrading were assessed in the present investigation. Acidity measurements by pyridine-adsorbed Fourier transformed infrared spectroscopy (FTIR) showed that hydroisomerization and aromatization activities were closely related to the density of acid sites and the ratios of medium Lewis acidity and strong Br?nsted acidity to total acidity. Compared with the single HZSM-5 supported catalyst, the single Hβ supported catalyst was found to have much better olefin reduction performance, but the product RON still suffered from a loss of 1.6. Compared to the single-zeolite supported catalysts, the binary-zeolite Hβ/HZSM-5 supported catalysts with the mass ratio of Hβ to HZSM-5 at 6.6 offered much more stable activity and selectivity to arene, which played an important role in preserving gasoline RON.     

Structural Evolution of Highly Active Ir-Based Catalysts for the Selective Reduction of NO with Reductants in Oxidizing Conditions

NO _x reduction over Ir-based catalysts in the presence of excess oxygen with hydrocarbon as a reductant was investigated in the focus on observing microstructure of Ir particle supported on various carriers and structural evolution of highly active Ir-based catalysts in the NO _x reduction. Characterization of Ir-based catalysts using SEM, TEM, XRD, CO chemisorption and XPS, and reaction studies on various Ir-based catalysts have proved that the formation of relatively large Ir metal particle with 40–60 nm of nanocrystal size carried on inert supports has been a prerequisite for the evolution of high activities in the NO _x reduction rather than the formation of Ir metal state on the catalyst. Furthermore, in inert gas conditions in a high temperature range of 850–950°C, Ir metal was easily formed by using the support such as TiO₂ and ZrO₂ that drastically decreased its specific surface area in the temperature range.