Synthesis and characterization of solid-phase super acid catalysts and their application for isomerization of n-alkanes
TL;DR: In this paper, the reference ACSZ-2 showed high activity toward isomerization of n-hexane, n-heptane, and n-octane into their corresponding branched chain isomers.
Abstract: In the present work, first, the reference catalyst super acidic nanostructured sulfated zirconia (SZ) and super acidic nanostructured aluminum chloride impregnated sulfated zirconium oxides in mole ratios of Zr4+:Al3+ as 2:1 (ACSZ-1), 1:1 (ACSZ-2), and 1:2 (ACSZ-3) were synthesized by a simple precipitation method. The catalytic performance of these four catalysts were evaluated during the isomerization of n-hexane, n-heptane, and n-octane to their corresponding branched chain isomers at low temperature and pressure conditions. ACSZ-2 shows high activity toward isomerization of n-hexane, n-heptane, and n-octane into their corresponding branched chain isomers. The reference catalyst SZ was proved to be less effective compare to the other three synthesized ACSZ catalysts. Ammonia-temperature-programmed desorption of these two materials ensures that the super acidity of ACSZ-2 is higher than that of SZ. Atomic force microscopic and scanning electron microscopic pictures predict the nature of the surf...
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TL;DR: In this article, a review of the recent advances in the development of bifunctional catalysts for n-alkane hydroisomerization is presented, as well as the catalytic behaviors and the reaction mechanisms over catalysts.
Abstract: The hydroisomerization of n-alkanes over bifunctional catalysts has played an increasingly important role in the modern petroleum industry due to its evident effects on the enhancement of the quality of fossil fuels. However, the preparation of bifunctional catalysts with excellent catalytic performance remains a significant challenge because of the complicated synergistic effects between the metal sites and Bronsted acid sites and the limited diffusion of alkene intermediates in the acid support. To overcome this challenge, the improvement of the metal–acid balance and the synthesis of hierarchical acid supports have become two commonly employed strategies. On the one hand, the favourable metal–acid balance is beneficial for the ideal consecutive hydroisomerization mechanism, which can be achieved by choosing the appropriate ratio of metal sites to Bronsted acid sites, controlling the nanoscale distance between two active sites, reducing the acidity and function of Bronsted acid sites, enhancing the function of metal sites and lowering the cost of preparation. On the other hand, via the “top down” (like desiliconization post-treatment) or “bottom up” (like templating methods) methods, the prepared hierarchical acid supports have more pore mouths or evidently reduced diffusion length. As a result, the alkene intermediates can either undergo isomerization at pore mouth instead of diffusing in the microporous channels or diffuse out fast from the short microporous channels, so that the diffusion limitation of alkene intermediates can be overcome and their cracking is inhibited. In this review, we summarize the recent advances in the developments of bifunctional catalysts for n-alkane hydroisomerization. The novel synthesis methods of the bifunctional catalysts are introduced, as well as the catalytic behaviours and the reaction mechanisms over catalysts. The effects of the metal–acid balance and the textural property on the catalytic performances are also discussed. The summarized studies reveal excellent potential for the design and preparation of novel bifunctional catalysts with excellent catalytic performances for n-alkane hydroisomerization.
37 citations
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TL;DR: The rich and stable interlayer porous biomass carbon sulfonic acids (SBCSAs) pillared by silica were prepared conveniently using bamboo powder and water glass as main raw materials and investigated.
Abstract: The rich and stable interlayer porous biomass carbon sulfonic acids (SBCSAs) pillared by silica were prepared conveniently using bamboo powder and water glass as main raw materials and investigated...
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TL;DR: In this paper , mesoporous KIT-6 support was synthesized hydrothermally and its structure was improved by impregnation with phosphotungstic acid (HPW), silicotungcial acid (HSiW), and some metals such as Pt, Pd, and Ce.
Abstract: In this study, mesoporous KIT-6 support was synthesized hydrothermally. Its structure was improved by impregnation with phosphotungstic acid (HPW), silicotungstic acid (HSiW), and some metals such as Pt, Pd, and Ce. This work converts mesoporous KIT-6 into a bifunctional catalyst containing acid and metal sites. The structures of the synthesized catalysts were characterized by various analyses such as XRD, XRF, FTIR, SEM, EDS, BET, NH3-TPD, and TGA. Furthermore, the catalytic performances of heteropoly acids (HPW and HSiW) and KIT-6 modified samples were investigated in an n-butane isomerization process. Impregnation of HSiW on mesoporous support resulted in higher initial n-butane conversion and isobutane selectivity and improved catalyst stability compared to the unsupported sample. The introduction of 0.5 wt % platinum on the 60%HSiW/KIT-6 led to the highest n-butane conversion (72%) and isobutane yield (56.8%) at 250 °C and weight hourly space velocity (WHSV) of 0.15 h–1, at the beginning of the reaction. The 0.5%Pt/60%HSiW/KIT-6 sample was the most stable catalyst against deactivation compared to other modified samples. Its conversion and its selectivity to isobutane reached 51.8 and 73.8%, respectively, after 7 h of reaction. Also, the influence of different process variables such as reaction temperature, WHSV, and carrier gas on the catalyst activity (n-butane conversion, isobutane selectivity, and yield) was investigated. In addition, the classical bifunctional model was used to describe the kinetic behavior of 0.5%Pt/60%HSiW/KIT-6 in the isomerization reaction. This model inhibits the hydrogen and n-butane pressure effects on the reaction rate and agrees with the ideal bifunctional metal–acid mechanism. The activation energy for this model was found to be 29.64 kJ mol–1. The classical bifunctional model provided a reasonable fit for the experimental data and allowed to specify the kinetic parameters.
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TL;DR: In this article, the potentiality of Pt and MoO3 loading on HBEA zeolite in enhancing n-heptane isomerization was investigated, and the results of in-situ FTIR studies of low-temperature hydrogen adsorption and n-Heptane adaption analyses help elucidate the isomerisation mechanism.
Abstract: The potentiality of Pt and MoO3 loading on HBEA zeolite in enhancing n-heptane isomerization was investigated. The multiple characterization techniques revealed the engagement of Pt and MoO3 on the lattice or defect structures of the HBEA framework. Furthermore, the occurrence of dealumination was confirmed by the existence of hydrated aluminium-molybdate, Al2-(MoO4)3. These findings proposed the presence of strong metal-support interactions. The n-heptane isomerization was comparatively investigated over Pt and MoO3 modified catalysts, and significantly higher rate of n-heptane conversion (0.059 μmol/g-cat m2 s) and rate of iso-heptane formation (0.026 μmol/g-cat m2 s) were achieved with Pt/MoO3-HBEA catalyst. The catalytic performance followed the order of Pt/MoO3-HBEA > MoO3-HBEA > Pt-HBEA > HBEA. It is anticipated that the results of in-situ FTIR studies of low-temperature hydrogen adsorption and n-heptane adsorption analyses help elucidate the isomerization mechanism and indicated there was a prerequisite for the presence of both Pt and MoO3 as dissociation and adsorption active sites for enhanced n-heptane isomerization. This study sheds light on the design of new type of MoO3 based catalysts for isomerization reaction.
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TL;DR: In this article , a new band at 1610 cm−1 of Zn/KCC-1, corresponds to the presence of Lewis acid sites and Brønsted acid sites.
Abstract: Fibrous silica (KCC-1) was impregnated with cobalt (Co), iron (Fe), and zinc (Zn) oxides which are denoted as Co/KCC-1, Fe/KCC-1 and Zn/KCC-1 for hydroisomerization of n-hexane. The characterization analysis revealed that the introduction of Co, Fe, and Zn into KCC-1 significantly altered the physicochemical properties of KCC-1 including reduced surface area, pore volume as well as crystallinity. Pyridine adsorbed IR showed that higher amount of the Lewis acid sites (LAS) and Brønsted acid sites (BAS) when introduced the Co, Fe, and Zn into KCC-1. Interestingly, a new band at 1610 cm−1 of Zn/KCC-1, corresponds to the presence of LAS by the formation of binuclear species of Zn in the form of [ZnOZn]2+. The formation of [ZnOZn]2+ was further confirmed by the presence of a band at 350 nm and higher intensity of the binding energy at 1022.8 eV from UV-DRS and XPS analysis, respectively. From temperature-programmed reduction analysis, these binuclear species were formed at a higher temperature, which has a stronger interaction with the KCC-1. The proposed formation of [ZnOZn]2+ was also discussed in this work. Based on the n-hexane hydroisomerization, the Zn/KCC-1 possessed the most excellent catalytic performance amongst the catalysts owing to the existence of the binuclear species of [ZnOZn]2+, which acts as a new acidic center in the stabilization of generated protonic acid sites by trapping of electrons, resulting in increased isomers yield of n-hexane as well as no cracking products. Zn/KCC-1 showed the lowest activation energy compared to other catalysts within 423–673 K.
References
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TL;DR: It was determined that in situ spectra of both schwertmannite and adsorbed sulfate are quite similar, suggesting that a continuum of outer- and inner-sphere sulfate occurs in both cases.
Abstract: The mechanism of sulfate adsorption on goethite was investigated in situ using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Sulfate adsorption was investigated at ionic strengths between 0.005 and 0.1 M, reactant concentrations between 5 and 500 μM, and pH values between 3.5 and 9.0. It was determined that sulfate forms both outer-sphere and inner-sphere surface complexes on goethite at pH less than 6. At pH values greater than 6, sulfate adsorbs on goethite only as an outer-sphere complex. The relative amount of outer-sphere sulfate surface complexation increased with decreasing ionic strength. The spectrum of sulfate adsorbed on goethite was also compared to the infrared spectrum of synthetic schwertmannite, an iron(III) oxy-hydroxy-sulfate. It was determined that in situ spectra of both schwertmannite and adsorbed sulfate are quite similar, suggesting that a continuum of outer- and inner-sphere sulfate occurs in both cases.
435 citations
"Synthesis and characterization of s..." refers background in this paper
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TL;DR: The catalytic properties of iron and manganese-promoted sulfated zirconia (SFMZ) for the isomerization of n-butane to isobutane are investigated using various catalyst pretreatments and reaction conditions.
Abstract: The catalytic properties of iron- and manganese-promoted sulfated zirconia (SFMZ) for the isomerization of n-butane to isobutane are investigated using various catalyst pretreatments and reaction conditions. The n-butane isomerization reactivity at 30{degrees}C is effected by calcination of the catalyst at 650{degrees}C in helium and vacuum treatment at room temperature indicating that superacidity is not likely to be responsible for activity. In addition, SFMZ samples exposed to dry air at over 450{degrees}C are more active than those calcined in helium at a reaction temperature of 30{degrees}C (n-butane conversions of 18.7% vs 0.4%) suggesting the presence of an active site involving a metal {open_quotes}oxy{close_quotes} species. The oxy species is capable of reacting CO to CO{sub 2} at room temperature and is present at a number density of 10-15 {mu}mol/g. At a reaction temperature of 100{degrees}C, SFMZ catalysts calcined in air then activated in helium show similar reactivities to those activated in air up to a preheating temperature of 450{degrees}C; above 450{degrees}C the metal oxy species is formed and provides additional activity (n-butane conversions of 37.1% in air vs 15.4% in He for calcinations at 650{degrees}C). The nature of the active sites on SFMZ are investigated using temperature-programmed desorption of substituted benzenes. Themore » liberation of CO{sub 2} and SO{sub 2} in the benzene TPD profile of SFMZ is attributed to the oxidation of benzene at the redox-active metal sites, resulting in the subsequent decomposition of the reduced iron (II) sulfate. Data from the TPD studies do not suggest the presence of superacidity on SFMZ that could contribute to the low-temperature n-butane isomerization activity. Instead, a bifunctional mechanism that involves a combination of a redox-active metal site and an acid site in close proximity is proposed. 62 refs., 17 figs., 4 tabs.« less
172 citations
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TL;DR: Al2O3-ZrO2 composite gel precursor powder containing 5-15 mol% ZrO 2 was prepared by wet chemical route in this paper, where the washed gel containing pseudoboehmite and amorphous zirconia was characterized with respect to DTA/TG, XRD and IR spectroscopy.
Abstract: Al2O3–ZrO2 composite gel precursor powder containing 5–15 mol% ZrO2 was prepared by wet chemical route. The washed gel containing pseudoboehmite and amorphous zirconia was characterized with respect to DTA/TG, XRD and IR spectroscopy. The DTA/TG result indicates three-stage decomposition for pseudoboehmite and single stage decomposition for amorphous zirconia. In the calcined powder phase evolution of Al2O3 follows the sequence pseudoboehmite ! bayerite ! boehmite ! g-Al2O3 ! u-Al2O3 ! a-Al2O3, while that of ZrO2 follows amorphous ZrO2 ! t-ZrO2 ! (t + m)ZrO2. FTIR studies revealed that the number of M–OH and M–O bond increase on increasing mol% of ZrO2 due to a change in the cationic charge of the composite powder. TEM photograph of calcined powder showed both dispersed nano-size spherical particle as well as agglomerated particles. EPMA confirmed the near uniform distribution of zirconia particles in the alumina matrix. # 2006 Published by Elsevier Ltd and Techna Group S.r.l.
171 citations
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TL;DR: The role of Pt in enhancement of catalytic activity is suggested to be caused by enhancement of the acid strength due to the coordination of PtO to SO groups as discussed by the authors.
Abstract: Our recent works on synthesis of solid superacids are reviewed. For evaluation of the surface acidity, temperature-programmed desorption of argon is proposed. For elucidation of the preparative conditions determining the catalytic activity, sulfated zirconias were prepared under different preparative conditions. The conditions varied were type of hydrated zirconia gel, drying temperature before sulfation, calcination temperature after sulfation. Although the optimum drying temperature and calcination temperature were different depending on the type of zirconia gel, the attainable activities were independent of the type of zirconia gel. We also modified sulfated zirconia by addition of Pt, Ru, and Fe to see the effects of the modification on the catalytic activity. The addition of Pt to sulfated zirconia resulted in an increase of the catalytic activity. The optimum amount of Pt-added was 7.5 wt.%. The optimum amount of Pt could be reduced to 3 wt.% when the catalyst was prepared by the double calcination method in which calcination procedures were performed both before and after impregnation with platinate solution. The role of Pt in enhancement of the catalytic activity is suggested to be caused by enhancement of the acid strength due to the coordination of PtO to SO groups. The catalytic activity of sulfated zirconia was also markedly enhanced by mechanically mixing with sulfated iron oxide. The enhancement was suggested to be caused by Fe 3+ acting as a reservoir for H − formed during the reaction.
126 citations
"Synthesis and characterization of s..." refers background in this paper
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