High Acid Site Density Research Articles

Investigation of carbon-based solid acid catalyst from Jatropha curcas biomass in biodiesel production

In this study, a carbon-based solid acid catalyst was prepared using the de-oiled Jatropha curcas (JC) seed cake waste. The catalyst was consequently used to esterify the JC oil in order to lower the high free fatty acid content (FFA) to an acceptable level (<4mgKOHg−1) for biodiesel production. The chemical and physical properties of the catalyst were characterized using a variety of techniques. The conversion of FFA reached 99.13% under optimum conditions of 12:1 methanol/oil molar ratio, 7.5wt% catalyst loading, 60min reaction time and 60°C reaction temperature at 350rpm. The catalyst was also determined to outperform the conventionally used sulfuric acid catalyst in terms of reaction time needed to achieve the highest conversion yield. The high catalytic ability of the catalyst was associated with the high acid site density formed in the catalyst which was due to the high porosity and large pore size of the carbon framework of the catalyst. The hydrophobic nature of the catalyst also contributed to the stability of the catalyst in which it can be re-used up until the 4th cycle. The recyclability of the catalyst and its cheap feedstock makes the overall process much simpler, cost-efficient and environment-friendly.

Octyl Co‐grafted PrSO3H/SBA‐15: Tunable Hydrophobic Solid Acid Catalysts for Acetic Acid Esterification

AbstractPropylsulfonic acid (PrSO3H) derivatised solid acid catalysts have been prepared by post‐modification of mesoporous SBA‐15 silica with mercaptopropyltrimethoxysilane (MPTMS), and the impact of co‐derivatisation with octyltrimethoxysilane (OTMS) groups to impart hydrophobicity to the catalyst was investigated. Turnover frequencies (TOFs) for acetic acid esterification with methanol increase with PrSO3H surface coverage across both families, suggesting a cooperative effect between adjacent acid sites at high acid site densities. Esterification activity is further promoted upon co‐functionalisation with hydrophobic octyl chains, with inverse gas chromatography (IGC) measurements indicating that the increased activity correlates with decreased surface polarity or increased hydrophobicity.

MOF-Derived Tungstated Zirconia as Strong Solid Acids toward High Catalytic Performance for Acetalization.

A strong solid acid, tungstated zirconia (WZ), has been prepared first using tungstate immobilized UiO-66 as precursors through a "double-solvent" impregnation method under mild calcination temperature. With moderate W contents, the as-synthesized WZ catalysts possess a high density of acid sites, and the proper heat treatment also has facilely led to a bunch of oligomeric tungsten clusters on stabilized tetragonal ZrO2. The resultant solid acids show an improved catalytic performance toward the benzaldehyde's acetalization in comparison with traditional zirconium hydroxide-prepared WZ. Notably, due to large surface area and additionally introduced strong acid sites, the MOF-derived WZ catalysts afforded conversion up to 86.0%. The facile method endows the WZ catalysts with superior catalytic activities and excellent recyclability, thus opening a new avenue for preparation of metal oxide-based solid superacids and superbases.

Preparation of NiAlO x and NiSiO x Complex Oxides with High Surface Areas for the Isomerization Reactions of 1-Hexene

The NiAlO x and NiSiO x complex oxides with high surface areas were prepared by the co-precipitation method through the control of acidity of solutions. Nickel species were found to be highly dispersed in these complex oxides and a remarkable feature was that the incorporation of large amount of nickel cations into SiO2 generated the great amount of surface acid sites. Upon the sulfidation by CS2, the sulfided catalysts were found to be highly active for the conversion of 1-hexene to different products formed from the three main competitive reactions (skeletal isomerization, double bond isomerization and hydrogenation of all hexenes). The high yield of skeletal isomerization of 1-hexene on a sulfided NiSiO x (55 %) could be attributed to the high density of acid sites for the adsorption of 1-hexene as well as the low hydrogenation activity of nickel species on this catalyst. In contrast, the high yields of direct hydrogenation and double bond isomerization of 1-hexene on the sulfided NiAlO x might be due to the high hydrogenation activity of nickel species as well as the surface acidity and basicity on the catalyst. The sulfided NiAlO x and NiSiO x complex oxides were highly active for the conversion of 1-hexene to different products. The high yield of skeletal isomerization of 1-hexene on the sulfided NS10 (55 %) could be attributed to the high density of acid sites for the adsorption of 1-hexene.

Support enhanced α-pinene isomerization over HPW/SBA-15

A family of mesoporous SBA-15 supported H3PW12O40 (HPW) catalysts were synthesized by wet-impregnation and compared with fumed silica analogues for the solventless isomerization of α-pinene under mild conditions. Structural and acidic properties of supported HPW materials were characterized by powder XRD, HRTEM, XPS, TGA, N2 porosimetry, DRIFTS, and ammonia and propylamine chemisorption and TPD. The high area, mesoporous SBA-15 architecture facilitates the formation of highly dispersed (isolated or low dimensional) HPW clusters and concomitant high acid site densities (up to 0.54mmolg−1) relative to fumed silica wherein large HPW crystallites are formed even at low HPW loadings. α-Pinene exhibits a volcano dependence on HPW loading over the SBA-15 support due to competition between the number and accessibility of acid sites to the non-polar reactant, with the superior acid site accessibility for HPW/SBA-15 conferring a 10-fold rate enhancement with respect to HPW/fumed silica and pure HPW. Monocyclic limonene and terpinolene products are favoured over polycyclic camphene and β-pinene by weaker polyoxometallate analogues over SBA-15.

A new catalyst for the solvent-free conversion of CO2 and epoxides into cyclic carbonate under mild conditions

A new Cu6 cluster [Cu6(μ4-O)2(SO4)4(DMA)6] (1) with high density of active Lewis acid sites turns out to be a good catalyst for the chemical fixation of CO2 into value-added cyclic carbonates without the use of any organic solvents under room temperature and atmospheric pressure. Above all, the preparation of 1 is very simple and rapid with low cost, which has important implications for industrial applications.

Synthesis of methanol and dimethyl ether from the CO2 hydrogenation over Cu·ZnO supported on Al2O3 and Nb2O5

We report the synthesis, characterization and catalytic evaluation of Cu·ZnO catalysts supported on Al2O3 and Nb2O5, as acidic materials, to study the CO2 hydrogenation to methanol and dimethyl ether. The catalysts were prepared by precipitation or impregnation of the metals over the supports. They were characterized by different techniques, such as XRF, BET area, TPD of n-butylamine, XRD and TPR. Catalytic tests were performed in an automated catalytic unit coupled to a gas chromatograph with FID and TCD detectors. Different conditions of temperature and pressure were studied. It could be observed that the choice of the synthesis method affects the activity and selectivity of the CO2 hydrogenation, at the conditions used in this work. The catalyst prepared by impregnation of the metals over the Al2O3 support was the most active and selective to dimethyl ether. This result can be explained by the better and lower temperature reducibility of CuO particles along with higher density of acid sites and strength of the alumina support.

Sulfated niobia supported on KIT-6 as a catalyst for transesterification of groundnut oil

Mesoporous 3D cubic KIT-6 was synthesised hydrothermally via organic template route. Different weight percentages (1, 2 and 3 %) of sulfated niobia were supported on KIT-6 by wet impregnation method and are abbreviated as 1SNK, 2SNK and 3SNK. The synthesised materials were characterized by XRD, FT-IR, BET surface area, DRS-UV Visible and TG techniques. The morphology of pure KIT-6 and SNKs were studied by SEM and HR TEM techniques. Experiments were performed with SNK catalysts for the transesterification reaction to convert the groundnut oil to fatty acid methyl ester (FAME). The product was confirmed by GC–MS. The parameters were optimized to increase the yield of FAME by altering the reaction temperature, reaction time, catalyst loading. Among the synthesized catalysts, 3SNK showed high activity than others due to high density of acid sites. Hence sulphated niobia supported KIT-6 may be better choice of catalyst for the conversion of groundnut oil to FAME.

Influence of acid site density on the three-staged MTH induction reaction over HZSM-5 zeolite

High acid site density can accelerate formation of active species and shorten the initial two stages of MTH induction reaction.

Synthesis of activated carbon based heterogenous acid catalyst for biodiesel preparation

The present work illustrates the synthesis of 4-sulfophenyl activated carbon based solid acid catalyst (ACPhSO3H), obtained from activated carbon (AC) by arylation with 4-sulfobenzenediazonium chloride. The variation of reaction conditions, such as, reaction temperature (20–85°C) and weight ratio of sulfanilic acid (precursor of 4-sulfobenzenediazonium chloride) to AC (0.14/1–14.00/1) provided ACPhSO3H with relatively high density of acid sites. The ACPhSO3H with the highest PhSO3H density (0.72mmol H+/g) was obtained using weight ratio of sulfanilic acid to AC (7.00/1) at 70°C after 10min. The catalyst was characterized by means of nitrogen adsorption analysis (average pore diameter 10.1nm, specific surface area 114m2/g, pore volume 0.29cm3/g), FT-IR, TG, XRD, FE-SEM and S elemental analysis. The spent catalyst can be easily regenerated recovering its initial density of acid sites. Upon employment in esterification reactions of rapeseed oil fatty acids, ACPhSO3H showed similar catalytic performance to Amberlyst-15.

Liquid phase dehydration of 1-indanol: Selective synthesis of indene over microporous acid catalysts

The selective dehydration of 1-indanol in liquid-phase was studied at 363 K and 2 bar, over solid acid catalysts, and using cyclohexane as a solvent. Mesoporous SiO2–Al2O3 with a high density of strong Lewis acid sites produced di-1-indanyl ether and other heavy products apart from indene. In contrast, the overall selectivity to indene with beta zeolite (HBEA, Si/Al = 12.5), HZSM-5 (Si/Al = 20) and dealuminated mordenite zeolite (HMOR, Si/Al = 80) was almost 100%. The transition state shape selectivity and a moderate density of both Lewis and Brønsted acid sites were crucial to achieve high selectivity to indene. In spite of the high overall selectivity, the final yield in indene with HBEA was only 55%. This was attributed to the formation of heavy compounds inside the large cavities of HBEA, which cannot diffuse through its micropores. In contrast, yields in indene higher than 90% were obtained with HMOR and HZSM-5. It was also observed that the yield in indene increased with time even after reaching the 1-indanol total conversion, which indicates the slow diffusion of the reactant and product molecules inside of the microporous network of HMOR and HZSM-5. Therefore, a process involving liquid phase dehydration of 1-indanol, employing one of these two zeolites as a catalyst would provide: 1) high yield in indene; 2) easy separation of product from solvent; 3) easy separation of the catalyst from the reaction medium.

Dehydration of glycerol to acrolein using H-ZSM5 zeolite modified by alkali treatment with NaOH

The dehydration of glycerol to acrolein has been studied using H-ZSM5 zeolite treated in alkaline medium in order to develop mesoporosity by desilication. Treatment of H-ZSM5 zeolite (Si/Al: 15) in NaOH solutions leads to mesoporosity development due to the preferential extraction of Si from the zeolite framework (desilication) without significant modification of the intrinsic zeolite properties. The samples were studied by powder X-ray diffraction (XRD), N2 adsorption, pyridine-temperature programmed desorption (Py-TPD) and FTIR of adsorbed pyridine. The coke deposits were analyzed by temperature programmed oxidation (TPO). The alkaline treatment conditions led to an increase in the mesopore surface area from 254m2g−1 for the calcined zeolite to 325m2g−1 for the alkaline-treated material, while the micropore volume was only slightly decreased (from 0.136 to 0.130mlg−1). Besides substantial mesoporosity development, the zeolite maintained Brønsted acidic properties, which are highly attractive in order to promote acid-catalyzed reactions like glycerol dehydration. Catalytic testing of the modified solids showed an improved performance in dehydration of glycerol to acrolein, due to the unique interplay between improved physical transport in the shortened micropores and the preserved high density of acid sites. The catalyst stability was improved upon desilication due to an increase in coke tolerance. A treatment of both solids in air at 773K led to a partial regeneration of acid sites for glycerol dehydration.

Production of renewable biofuels and chemicals by processing bio-feedstock in conventional petroleum refineries

The influence of catalyst characteristics, i.e., acidity and porosity on the product distribution in the cracking of triglyceride-rich biomass under fluid catalytic cracking (FCC) conditions is reported. It has found that the degradation degree of triglyceride molecules is strongly dependent on the catalysts’ acidity. The higher density of acid sites enhances the conversion of triglycerides to lighter products such as gaseous products and gasoline-range hydrocarbons. The formation of gasoline-range aromatics and light olefins (propene and ethene) is favored in the medium pore channel of H-ZSM-5. On the other hand, heavier olefins such as gasoline-range and C4 olefins are formed preferentially in the large pore structure of zeolite Y based FCC catalyst (Midas-BSR). With both catalysts, triglyceride molecules are mainly converted to a mixture of hydrocarbons, which can be used as liquid fuels and platform chemicals. Hence, the utilization of the existing FCC units in conventional petroleum refineries for processing of triglyceride based feedstock, in particular waste cooking oil may open the way for production of renewable liquid fuels and chemicals in the near future.&#x0D; Bài báo trình bày kết quả nghiên cứu khả năng tích hợp sản xuất nhiên liệu sinh học và hóa phẩm từ nguồn nguyên liệu tái tạo sinh khối giầu triglyceride bằng công nghệ cracking xúc tác tấng sôi (FCC) trong nhà máy lọc dầu. Kết quả nghiên cứu cho thấy xúc tác có ảnh hưởng mạnh đến hiệu quả chuyển hóa triglyceride thành hydrocarbon. Tính acid của xúc tác càng mạnh thì độ chuyển hóa càng cao và thu được nhiều sản phẩm nhẹ hơn như xăng và các olefin nhẹ. Xúc tác vi mao quản trung bình như H-ZSM-5 có độ chọn lọc cao với hợp chất vòng thơm thuộc phân đoạn xăng và olefin nhẹ như propylen và ethylen. Với kích thước vi mao quản lớn, xúc tác công nghiệp FCC dựa trên zeolite Y ưu tiên hình thành C4 olefins và các olefin trong phân đoạn xăng. Ở điều kiện phản ứng của quá trình FCC, triglyceride chuyển hóa hiệu quả thành hydrocarbon mà có thể sử dụng làm xăng sinh học cho động cơ và olefin nhẹ làm nguyên liệu cho tổng hợp hóa dầu.

Study of the influence of physical–chemical properties of steamed H-MOR zeolites in the mechanism of adsorption of fatty acids and their esterification

The increasing use of fatty acid esters, on the industry and the substitution of traditional petroleum fuels, promotes the study of heterogeneous catalysts with a better environmental performance than their homogeneous counterparts. The mordenite, has attracted special attention, for its environmental friendliness, exceptional physical chemical properties and the availability of large natural deposits. In order to study the influence of its physical chemical properties over the mechanism of adsorption of fatty acids (FA) and their esterification, three new solids were obtained through hydrothermal treatment at 800–1000K of a mordenite with a Si/Al ratio of about six. The characterization by FTIR and XRD confirms the collapse of crystallinity with the increase of the treatment temperature. The partial exiting of tetrahedral aluminum out of the crystalline network, revealed by 29Si and 27Al MAS NMR leads to the diminution of the acidity and the increasing hydrophobicity, evidenced by FTIR spectroscopy and adsorption isotherms of stearic acid. The kinetic evaluation of FA esterification reveals a pseudo-second order model. These results suggest a change in the adsorption mechanism: In the original mordenite and treated at low temperatures, a higher density of acid sites favors the adsorption of the carboxyl group of FA molecules by hydrogen-bonding to the zeolite Al–OH–Si groups, while the tails adsorb on the less polar surroundings. At greater treatment temperatures, the taller hydrophobicity induces the adsorption of the FA molecules onto the lesser polar (and lesser active) sites of the zeolite with its carboxyl groups oriented away from the zeolitic surface.

MCM-41 Supports Modified by Al, Zr and Ti for NiW Hydrodenitrogenation Catalysts

MCM-41 materials modified by Al, Zr and Ti were used as supports for the preparation of the NiW hydrodenitrogenation (HDN) catalysts. The modified supports, with highly dispersed Al, Zr and Ti species and without loss of the MCM-41 characteristics, can be prepared by a postsynthetic method. The incorporation of Al, Zr and Ti can enhance the density of acid sites on the modified MCM-41, so as to increase the density of acid sites and even enhance the dispersion of Ni, W species on the corresponding catalysts. The HDN results showed that the incorporation of Al, Zr and Ti can increase the HDN activity of the catalysts and the activity followed the order of Ni/W/Al > Ni/W/Zr > Ni/W/Ti > Ni/W. The high HDN activity of Ni/W/Al ascribed to the high density of acid sites and the well dispersion of the Ni and W species on the catalyst.

Effects of method of preparation on catalytic activity of Co–Zn double-metal cyanide catalysts for copolymerization of CO2 and epoxide

Co–Zn double-metal cyanide (DMC) complexes are well-known catalysts for ring-opening polymerization of epoxides and co-polymerization of CO2 and epoxides. This work provides an insight on structure–activity relationship of DMC for poly(cyclohexene carbonate) synthesis. Seven samples of DMC were prepared by different methods and mode of reagent addition. Highly active catalyst could be synthesized even without using a co-complexing agent. CO2 adsorption studies revealed that higher the guest-host interaction higher would be the catalytic activity. High density and strength of Lewis acid sites, moderate crystallinity, low crystal symmetry (rhombohedral/monoclinic), Cl− ions and coordinated tert.-butanol (complexing agent) control the catalytic activity for polycarbonates. Chloride in the structure avoided induction period by increasing acidity of the catalyst and thereby, improving the guest–host interactions. Polycarbonates with CO2 incorporation as high as 86mol%, average molecular weight of 20900 and polydispersity index of 1.8 were prepared at complete conversion of cyclohexene oxide.

Catalytic production of oxygenated additives by glycerol etherification

Abstract In this work the etherification reaction of glycerol with isobutene (IB) and tert-butyl alcohol (TBA) has been studied with the aim of preparing mixtures with high content of poly-substituted ethers. The results obtained using solid acid catalysts have shown that the reaction with IB proceeds at a high rate but the formation of undesired di-isobutene (DIB) represents a serious problem when catalysts with high density of acid sites, such as Amberlyst, are used. When using TBA as a reactant, the main problem is the formation of water that, due to thermodynamic reasons, prevents the formation of poly-substituted ethers regardless of the catalyst used. Some preliminary experiments carried out with a water permselective tubular membrane have demonstrated that the yield of poly-substituted ethers significantly increases once water was selectively removed from the reaction medium by recirculation of the gas phase.

Titania as an Early Transition Metal Oxide with a High Density of Lewis Acid Sites Workable in Water

Anatase TiO2 prepared by a simple sol–gel reaction of Ti(i-pro)4 was studied as an early transition metal oxide with Lewis acid sites workable in water. Fourier transform infrared (FT-IR) measurements revealed that TiO2 has a significantly higher density of effective Lewis acid sites in water than niobic acid (Nb2O5·nH2O), a heterogeneous water-tolerant Lewis acid, because most Lewis acid sites on TiO2 can maintain Lewis acidity even in the presence of water, which is in contrast to those on Nb2O5·nH2O. TiO2 as an easily separable and reusable heterogeneous catalyst that exhibits higher catalytic performance for the transformation of pyruvaldehyde into lactic acid and the allylation of benzaldehyde with tetraallyltin in water than Nb2O5·nH2O, and the catalytic activity of TiO2 is comparable to that of scandium trifluoromethanesulfonate (Sc(OTf)3), a highly active homogeneous water-tolerant Lewis acid, despite the lower amount of effective Lewis acid sites. The high catalytic performance of TiO2 for these reactions can be attributed to a high density of Lewis acid sites that can function in water.

Solvent free synthesis of coumarin derivative by the use of AlSBA-1 molecular sieves

AlSBA-1 molecular sieves were synthesized successfully and used for the synthesis of coumarins through Pechmann condensation. The synthesized AlSBA-1 catalysts were characterized by XRD, BET, SEM, FTIR, TGA techniques. The synthesized materials possess large surface area with mesopores. Pechmann condensation of 3-methoxyphenol and ethyl acetoacetate was carried out under solvent free condition and 7-methoxy-4-methylcoumarin was the main product. The selectivity of the product was found to be 74.04%. Among the synthesized catalysts, AlSBA-1(2) showed high activity than others due to high density of acid sites. Hence, AlSBA-1 molecular sieves a better choice of catalyst for the synthesis of coumarins.

Carbon-coated mesoporous silica functionalized with sulfonic acid groups and its application to acetalization

The inner surface of mesoporous silica SBA–15 was coated by a homogeneous polycyclic carbon layer through controlled carbonization of furfuryl alcohol. The composite was subsequently functionalized with sulfonic acid (−SO3H) groups to form a strong solid acid material, with a tunable acid site density in the range of 0.38–0.84 mmol/g by varying the thickness of the carbon layer. Structural analysis and reaction data revealed that the solid acid catalyst exhibited high reactivity towards the acetalization of aldehydes or ketones with alcohols because of the uniform carbon coating of the mesopores, high acid site density, and its mechanical stability. 采用浸渍法将糠醇负载在铝改性的SBA-15介孔孔道中, 经550 °C不完全碳化制备了结构规整、含多苯环的中空管状硅碳复合介孔材料. 结果表明, 通过温和磺酸化作用可使磺酸基团成功取代在多苯环上, 其酸量随着多苯环涂层厚度变化在0.38∼0.84 mmol/g范围内可控调变. 相比于蔗糖作为糖源的复合固体酸, 所制碳多苯环-硅酸催化剂具有中空碳纳米管堆积的类似CMK-5介孔结构, 以及较大的反应空间、稳定的机械性能、较高的比表面和大量可以接触的质子酸中心, 因而在大分子缩醛(酮)反应中表现了良好的催化性能.