Search

With the overview of different kinds of phenol synthesis routes, dehydrogenation of cyclohexanone to phenol under sub-critical water condition using Pt, Pd, Rh, Ru and Re immobilized heterogeneous catalysts have been reported. Surface properties and characterizations of the catalysts were done. Binding of metal on a support and their relationship with zeta potential (ζ) and their effect on catalytic activity are discussed. Importance of sub-critical water reaction conditions in terms of thermodynamic favourability and phase equilibrium are evaluated through ASPEN simulator. Based on the results obtained, possible reaction pathways for the formation of product and the by-products are illustrated. The feasibility of a metal acting as a dehydrogenation catalyst according to M0/MII (E0) couple is also explained.

Abstract Removal of trace olefins from aromatic liquids was investigated on UZM-8 and MCM-22, which are the family of MWW zeolites. Both these zeolites were synthesized with similar Si/Al ratio and characterized by various techniques such as XRD, SEM, ICP, N2 adsorption, Ammonia TPD and solid-state MAS-NMR. Olefin conversion activity over UZM-8 was found to be significantly higher than that of MCM-22. In addition to this, deactivation of UZM-8 was slower than the MCM-22. UZM-8 with irregular stacking of MWW layers possess high external surface area and exposes more number of active sites to the reactant molecules. Mesopores generated due to the disordered layers of UZM-8 allows the fast diffusion of the substrate molecules in which pore clogging does not occur, thus making it more active and slow deactivation than that of MCM-22. Graphic abstract

Cerium incorporated MCM-22 (Ce-MCM-22) was successfully synthesized by hydrothermal method. Incorporation of Ce is achieved by the optimization of method for synthesis by varying (i) Concentration of sructure directing agent or template, (ii) Silica to ceria ratio and (iii) Crystallization time. Change in phases during crystallization, variation of physico-chemical properties with respect to gel composition and framework substitution of cerium are evidenced by XRD, UV–Vis DRS, SEM, N2 adsorption, FT-IR, Ammonia TPD and solid-state MAS-NMR characterisations. It is found that incorporation of Ce into the zeolite frame work has successfully occurred by simple method of optimisimg molar gel composition. Interestingly, prepared samples of Ce-MCM-22 have also been found to be more effective catalysts for the removal of trace olefins from aromatic streams.

Silicate anion forms four, five and six coordinate complexes with chiral polyhydroxy alcohol and polyhydroxy acids in aqueous alkali media. The chemistry of organosilicate complexes is well established but its effect on zeolite synthesis has not been explored. When chiral acid is used as a template in ZSM-5 synthesis, a new partially crystalline layered silicate is formed whose basal spacing value do not match with any of the known layered silicates. Chiral acids are necessary to induce layered silicate formation and it is not formed in absence of any template or tetrapropylammonium bromide (TPABr) as a template. In presence of chiral acid, layered silicates are not precursors to ZSM-5 formation as observed normally in ZSM-5 synthesis. This method is new and it paves the way for generating layered silicates using simple chiral acids as a template.

Very high surface area Au-SBA-15 type materials containing gold nanostructures were synthesised by oxidatively polymerizing aniline using chloroauric acid concurrently with condensing silicate in the presence of a triblock copolymer. The aforementioned synthesis resulted in significant changes to the morphology, texture, density and surface properties of the gold loaded materials as compared to SBA-15 prepared using a very similar method. The surface area of all of the prepared gold loaded materials was significantly higher than the parent SBA-15, with one material having an extremely high surface area that was more than double the parent SBA-15 (1424 m2 g−1 vs 640 m2 g−1). Characterisation of the gold loaded materials with small and wide angle X-ray diffraction, N2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermo gravimetric analysis (TGA), infrared spectroscopy (FTIR), and diffuse reflectance UV–vis spectroscopy revealed that the prepared gold containing SBA-15 materials were ordered and that they contained two distinct sizes of gold nanoparticles (∼40 nm and ∼3–5 nm). High resolution TEM images of prepared materials that had been etched using potassium hydroxide showed that the smaller gold nanoparticles were incorporated within the walls of the mesoporous silica.

Advantages of confining the gold nanostructures formation within the mesoporous silica pore walls during its silica condensation and consequent improvement in the textural properties such as specific surface area, pore volume, pore diameter have been demonstrated, while retaining gold nanostructures within the silica walls. This has been achieved by tryptophan mediated confinement of gold nanoparticles formation within the condensing silica framework, to obtain Au–SBA-15 (SSA 1247 m2/g, Vt ∼ 1.37 cm3/g) and Au–MCM-41 (SSA 1287 m2/g, Vt ∼ 1.1 cm3/g), mesoporous silica materials having the combination of very high surface area from the porous support as well as gold nanoparticles infiltrated silica walls. Choice of tryptophan for this purpose is that it has an indole group, which was known to reduce gold ions to form gold nanoparticles and its amine and carboxylic acid groups, catalyze the hydrolysis of silica precursors in a wide range of pH. These properties have been utilized in restricting the gold nanostructures formation inside the condensing silica phase without affecting the self assembly between the silica precursors and the triblock copolymer (for SBA-15) or cetyltrimethylammonium bromide template (for MCM-41). The polytryptophan and the gold nanostructures, which were encapsulated within the silica framework and upon removal of the template by calcination resulting in the formation mesoporous materials wherein the silica walls become microporous due to the removal of occluded polytryptophan and the resulting microchannels contain very small gold nanostructures. Hence, the resulting materials have very high surface area, high pore volume and narrow pore size distribution as compared to their parent SBA-15, MCM-41 and SBA-15, MCM-41 post functionalized with gold nanoparticles inside the pores.

Ni-nanoparticle supported on mesoporous ZSM-5 was prepared by dispersing colloidal Ni-nanoparticle over mesoporous ZSM-5. The resulting material was found thermally stable even at 900 °C and has uniform pore diameter of around 5 nm. The material was characterized by XRD, FE-SEM, TEM, XPS, TPR and N 2 adsorption/desorption. Reforming of methane with CO 2 was performed over Ni supported on mesoporous ZSM-5 at atmospheric pressure. The catalyst shows 96.2% methane conversion at 800 °C with the production of synthetic gas with the H 2 /CO mole ratio of 1:1. Various reaction parameters like temperature, weight hour space velocity (WHSV), Ni loading and time on stream were also studied.

The influence of Yb on Ni(20 wt%)/γ-Al 2 O 3 catalysts (prepared via a sol–gel method) for use in the dry reforming of methane was investigated. It was found that the addition of low quantities of Yb (1–2 wt%) led to significant increases in catalytic activity and catalyst stability, and the production of H 2 and CO at a ratio close to unity (∼0.95). Higher levels of Yb doping (3–8 wt%) did not achieve similar increases in activity as those observed in the lower level doped catalysts. Based on characterisation studies conducted on the catalysts before and after testing it was found that the catalyst with a low level of Yb (2 wt%) had the smallest average Ni particle size, narrowest particle size distribution and highest ease of reducibility (based on Temperature Programmed Reduction analysis). Analysis of the catalysts after testing showed that the catalyst with 2 wt% Yb also experienced the lowest level of carbon deposition and contained a high degree of graphitised carbon. The results obtained indicate that doping of Ni-Al 2 O 3 catalysts with a select amount of Yb can give rise to a catalyst with excellent properties for use in the dry reforming of methane and that Yb can have a significant role in controlling the size/mobility of Ni nanoparticles produced via reduction of NiO.

Nanostructured Ni-incorporated mesoporous alumina (MAl) materials with different Ni loading (7, 10 and 15 wt %) were prepared by a template assisted hydrothermal synthesis method and tested as catalysts for CO2 reforming of methane under different conditions (nickel loading, gas hourly space velocity (GHSV), reaction temperature and time-on-stream (TOS)). The most active catalyst tested (Ni(10 wt%)-MAl) showed a very high stability over 200 h compared to a Ni(10 wt%)/γ-Al2O3 prepared using a co-precipitation method which had a significant loss in activity after only ∼4 h of testing. The high stability of the Ni-MAl materials prepared by the template assisted method was due to the Ni nanoparticles in these catalysts being highly stable towards migration/sintering under the reaction conditions used (800 °C, 52,000 mL h−1 g−1). The low susceptibility of the Ni nanoparticles in these catalysts to migration/sintering was most likely due to a strong Ni-support interaction and/or active metal particles being confined to the mesoporous channels of the support. The Ni-MAl catalysts also had significantly lower amounts of carbon deposited compared to the catalyst prepared using the co-precipitation method.

A variety of multivalent metal salt, many of them are hydrates, were screened as catalysts for the esterification of fatty acids and alcohols. These salts included chlorides, nitrates, sulfates, and acetates of Fe3+, Al3+, Ga3+, In3+, ZrO2+, HfO2+, Zn2+, Co2+, Ni2+, Mn3+, Cr3+, and Cu2+. Ferric salts, particularly, FeCl3·6H2O, were the most active among the salts screened. The esters of primary C10−C18 fatty acids and alcohols were obtained quantitatively from equimolar mixtures in the presence of FeCl3·6H2O (substrate/catalyst (S/C; mol/mol) = 200, reaction period = 6 h, in refluxing mesitylene). Esters of isostearic acid and C10–C18 fatty alcohols were obtained with large quantities and prolonged reaction periods. The esters of aromatic carboxylic acids with cetyl alcohol and bulky steroid alcohols, including cholesterol, with C8−C18 fatty acids, were obtained in high yield. The cationic cluster formed by hydrolysis of the ferric cation is proposed to be the catalytically active species. Such a catalysi...

Some typical multi-valent metal salt hydrates, such as chloride, nitrate, sulfate, and acetate of Fe3+, Al3+, Ga3+, In3+, ZrO2+, HfO2+, Zn2+, Co2+, Ni2+, Mn3+, Cr3+, and Cu2+ have catalytic activities for the esterification of saturated and unsaturated fatty acids and alcohols. Supporting these metal salt hydrates on ordered mesoporous silica such as MCM-41 enhanced the catalytic activity of the esterification. The esters of C10-C18 normal acid and alcohol were obtained in high yield by some of supported metal salt hydrates on MCM-41; however, the yield of the esters decreased with their chain length of acids and alcohols although the activities depended on type of metal salt hydrates. The catalyst is recyclable although some loss of activity was observed.

Friedel–Crafts alkylation of aromatics with benzyl alcohol as alkylating agent has been investigated over rare earth metal triflates, Sc(OTf)3, Hf(OTf)4, La(OTf)3, and Yb(OTf)3 supported on MCM-41. The catalytic activity of triflates, particularly, Sc(OTf)3 and Hf(OTf)4 was enhanced by being loaded onto MCM-41 because of increased dispersion, and gave the benzylated product in high yield. They were reusable without the loss of the activity for their recycling. Water generated during the benzylation with benzyl alcohol (BnOH) did not affect on the catalytic activity of the Sc(OTf)3 supported on MCM-41 (Sc(OTf)3/MCM-41). The catalytic activity of Sc(OTf)3/MCM-41 was not affected by the further addition of water equimolar to BnOH. The benzylation of aromatics (toluene, p-xylene, mesitylene, and naphthalene) with benzyl alcohol, and of benzene with benzyl alcohols (4-methylbenzyl alcohol and 4-chlorobenzyl alcohol) were studied over Sc(OTf)3/MCM-41 at 353 K. The rate of the benzylation of benzene over Sc(OTf)3/MCM-41 was accelerated by electron donating groups and retarded by electron withdrawing groups. The benzylation of aromatics proceeds with direct benzylation with benzyl alcohol, and the dehydration product, i.e., dibenzyl ether (DBE), which is a by-product formed during the benzylation of aromatics; however, it participates in the benzylation with benzene via BnOH with the decrease in BnOH.

Direct condensation of equimolar amounts of long chain carboxylic acids and alcohols could be achieved by using zirconyl chloride as an efficient catalyst. ZrOCl 2 .8H 2 O showed high activity for esterification between primary acids and alcohols; however, it was less active in the combination of branched acid and secondary alcohols to give the corresponding esters.

Samples of small-pore Engelhard titanium silicate ETS-4 and its Sr-exchanged variant, patented by Engelhard Corporation, were successfully synthesized in our laboratory, and the characteristic signatures of their crystal structures were confirmed by X-ray diffraction (XRD). Thermogravimetric analysis (TGA) was carried out to study their thermal behavior and stability, and crystal morphology was examined using a scanning electron microscope (SEM). The synthesized fine crystals were pelletized by pressure binding without the addition of any binder material. Equilibrium and uptake measurements for oxygen, nitrogen, and methane on Na- and Sr-exchanged ETS-4 were then carried out in a constant-volume apparatus. The equilibrium capacities of the three gases in the Na form of ETS-4 were comparable, and Sr exchange did not seem to significantly affect these capacities. However, Sr exchange appreciably increased the uptake rate of nitrogen and reduced that of methane, thereby increasing the kinetic selectivity to a promising level. Capacity and uptake measurements were also conducted on the Sr-exchanged ETS-4 dehydrated at different temperatures. It was observed that increasing dehydration temperature progressively lowered the capacities and also slowed the kinetics of adsorption. Probable reasons for the observed changes in equilibrium capacity and uptake are discussed in detail.

A liquid phase reaction between anhydrous AlCl3 and terminal Si–OH groups of mesoporous Si-MCM-41 in dry CCl4 results in a AlClx-grafted Si-MCM-41 (with Cl/Al ratio=1.43, Al(tetrahedral)/Al(octahedral)=ratio=0.84 and Al/Si ratio=0.17). This catalyst shows high catalytic activity in Friedel–Crafts type benzylation (by benzyl chloride) and acylation (by benzoyl chloride) of benzene and toluene.

Thermal activation of clayzic catalyst has been thoroughly investigated by calcining anhydrous ZnCl2 impregnated on Mont-K10 with different ZnCl2 loadings (0.5-2.0 mmol g-1) under static or flowing air at 270 °C and also under N2 flow at different temperatures (150-400 °C). Depending upon the ZnCl2 loading and calcination temperatures, an appreciable amount of HCl is evolved in the thermal activation, indicating an occurrence of reaction between the ZnCl2 and the surface hydroxyl groups of the clay (- OH + ZnCl2→ - O - Zn - Cl + HCl), leading to formation of new Lewis acid sites (- O - Zn -Cl). The Cl/Zn ratio, surface area and catalytic activity (in the benzene benzylation by benzyl chloride at 80 °C) of the clayzic formed in the thermal activation are influenced markedly by the ZnCl2 loading and calcination conditions (temperature and gas atmosphere). The maximum catalytic activity for the clayzic is observed at the optimum ZnCl2 loading (about 1.0 mmol g-1) and calcination temperature (about 270 °C). The thermal activation at 270 °C under flowing N2 led to a most active clayzic catalyst for the benzene benzylation. A temperature-programmed evolution of HCl in the calcination of ZnCl2/Mont-K10 with different ZnCl2 loadings from 25 to 400 °C at a linear heating rate of 2 °C min-1 has also been investigated.

Grafting of AlCl3 onto Si–MCM-41 using the reaction of anhydrous AlCl3 from its CCl4 solution with terminal Si–OH groups of Si–MCM-41 under reflux at two different concentrations of AlCl3 relative to Si–MCM-41 has been studied. The influence of thermal-treatment conditions (viz., temperature and gas atmosphere, such as vacuum, static or flowing air, and flowing N2) on bulk and surface properties of the AlCl3-grafted Si–MCM-41 has also been investigated. The AlCl3-grafted Si–MCM-41 samples before and after thermal treatment were characterized by Fourier transform infrared, 27Al magic-angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, and energy disperse X-ray analysis (EDAX) analysis and also for their surface area and concentration of strong acid sites (measured in terms of the pyridine chemisorbed at 400°C). The incorporation of tetrahedral Al in the MCM-41 structure with the creation of strong acid sites could be accomplished by thermally treating the AlCl3-grafted Si–MCM-41, particularly in a flow of N2 at 400°C.

Si-MCM-41 supported InCl3, GaCl3, FeCl3 and ZnCl2 catalysts (metal chloride loading = 1.1 mmol g −1 ) have very small activity for the dehydration of tert-butanol and hence show very high selectivity (>99%) for the esterification of tert-butanol by acetic anhydride, producing acetic acid as a by-product, at ⩽50°C. The esterification activity of the supported metal chloride catalysts is in the following order: InCl3> GaCl3> ZnCl2> FeCl3.

Adsorption properties of the mesoporous H–AlSi–MCM-41 and Na–AlSi–MCM-41 materials for aromatic hydrocarbons have been investigated by studying the temperature programmed desorption (TPD) of toluene, p-xylene, mesitylene and naphthalene over the mesoporous materials from 323 to 673 K at different linear heating rates (5–25 K min−1). The toluene TPD spectra show three distinct peaks for the H–AlSi–MCM-41 but a single asymmetric peak with humps for the Na–AlSi–MCM-41. The TPD spectra of all the other aromatic hydrocarbons for both the adsorbents show a single asymmetric peak with humps. The order of the heat of adsorption for the aromatic hydrocarbons, estimated from the temperature dependence of their peak (first one) maximum temperature was found as follows: toluene

Clay (kaolin, mont-K10 and mont-KSF) supported InCl 3 , GaCl 3 , FeCl 3 and ZnCl 2 catalysts (metal chloride loading=1.1 mmol g −1 ) show high selectivity (⩾98%) at high conversion in the esterification of tert-butanol by acetic anhydride to tert-butyl acetate ( t -BA) and very low activity for the dehydration of tert-butanol at ⩽50°C. For all the catalysts, mont-K10 is the best support and the order of their esterification activity (at 26°C) is: InCl 3 /mont-K10 (TOF=0.025 s −1 ) > GaCl 3 /mont-K10 (0.023 s −1 ) > FeCl 3 /mont-K10 (0.02 s −1 ) ⩾ ZnCl 2 /mont-K10 (0.019 s −1 ). InCl 3 /mont-K10 is highly active, selective and reusable catalyst for the esterification.

Temperature programmed desorption (TPD) of aromatic hydrocarbons (viz. toluene, p -xylene, mesitylene and naphthalene) on mesoporous high silica MCM-41 from 323 to 673 K at different linear heating rates (5, 10, 15 and 25 K min −1 ) has been investigated. TPD of toluene at different adsorbate loading (0.5 to 16.3 μmol g −1 ) has also been investigated. All the TPD curves have a single asymmetric peak. The heats of adsorption of aromatic hydrocarbons on the mesoporous material, estimated from the TPD peak maximum temperatures measured at different heating rates, was found to occur in the following order: toluene p -xylene H a increases with the decrease in the ionization potential of the hydrocarbons. The adsorption results from weak interactions between the π-electrons of aromatic hydrocarbons and the terminal poorly acidic silanol (Si–OH) groups. In the case of toluene TPD, the TPD peak maximum temperature increases with decreasing the adsorbate loading, indicating the presence of site energy distribution on the high silica MCM-41.

Adsorption isotherms of benzene, toluene, p-xylene, and mesitylene on high-silica MCM-41 (Si−MCM-41) at different temperatures (348−498 K) have been studied using gas chromatographic technique (GC peak maxima method). The Freundlich adsorption model fits the adsorption data for the aromatic hydrocarbons at all the temperatures. The isosteric heats of adsorption of the aromatic hydrocarbons at different loadings, obtained from the adsorption isotherms, are found to be in the following order: Qa (benzene) < Qa (toluene) < Qa (p-xylene) < Qa (mesitylene). The heat of adsorption of all the aromatic hydrocarbons is decreased with increasing the adsorbate loading; the decrease for the benzene adsorption at intermediate adsorbate loading is found to be more pronounced, indicating induced surface heterogeneity due to the presence of adsorbed benzene. Entropy analysis of the adsorption indicated that the adsorbed aromatic hydrocarbons (except benzene at very low adsorbate loading) are neither completely mobile no...

The influence of zeolite factors, such as Ga loading (0–3%), Si/Al ratio (35–132), degree of H + exchange (2–98%) and calcination temperature (600–800°C), affecting zeolitic acidity on the activity and selectivity of Ga/H–ZSM-5 in the aromatization of propane has been investigated. The activity and selectivity in propane-to-aromatics conversion are found to be influenced strongly by the above zeolite factors. The aromatization activity and selectivity of the zeolite shows a close relationship with its strong acidity (measured in terms of pyridine chemisorbed at 400°C). The propane aromatization activity and selectivity increases sharply with the increase in the strong acid sites of the Ga/H–ZSM-5.

The acidity and initial and time-on-stream activity in propane aromatization (at 550°C, space velocity of 3100 cm3g−1(zeolite)h−1) of Ga-impregnated H-ZSM-5 zeolite without or with binders (50 wt%), such as silica, alumina and kaolin, have been investigated. Both the acidity and catalytic activity of the zeolite are influenced by the presence of binder in the catalyst, depending upon the binder. The influence is found to be lowest for alumina and highest for kaolin. Among the binders, alumina is the most preferred binder for the zeolite catalyst.

The influence of zeolite factors such as pore geometry (viz. H-USY, H-BEA, H-MOR, H-ZSM-5) and Si/Al ratio and reaction conditions such as feed flow rate (liquid hourly space velocity, LHSV = 57.6, 115, and 230 h −1 ), feed composition (molar ratio: allyl acetate/bromobenzene = 1/10, 1/20, 1/40, 1/100, and 1/150) and reaction temperature (130, 150, and 170 °C) in the alkylation of bromobenzene with allyl acetate has been investigated. The activity and selectivity in allyl acetate to alkylated products conversion are found to be strongly influenced by the zeolite factors. Catalysts with smaller pore sizes deactivate faster due to faster pore blocking by side products. H-USY zeolites deactivate the slowest and produce the largest amount of alkylation products. The distribution for the total alkylation products (consisting of allyl bromobenzene (ABB), cis - and trans -propenyl bromobenzene (PBB) and dialkylated product (DAP)) lies around 50% over the whole allyl acetate conversion range with H-USY. H-MOR and H-ZSM-5 produce practically no primary alkylation products, but rather a large amount of side products of the alkylating agent. The conversion of allyl acetate decreases with increasing liquid hourly space velocity and allyl acetate concentration in the feed. At high concentration of allyl acetate, the formation of light components is high. Higher reactor temperatures lead to higher initial catalyst activity, but also faster deactivation and lower selectivity for alkylation products.

Direct condensation of equimolar amounts of long chain carboxylic acids and alcohols could be achieved by using zirconyl chloride as an efficient catalyst. ZrOCl 2 .8H 2 O showed high activity for esterification between primary acids and alcohols; however, it was less active in the combination of branched acid and secondary alcohols to give the corresponding esters.

Some typical multi-valent metal salts, such as chloride, nitrate, sulfate, and acetate of Fe(III), Al(III), Ga(III), In(III), Zr(IV), Hf(IV), Zn(II), Co(II), Ni(II), Mn(III), Cr(III), and Cu(II) ha...

ZrOCl2·8H2O is an efficient catalyst for the esterification of long chain carboxylic acids with long chain primary and secondary alcohols. Supporting ZrOCl2·8H2O on ordered mesoporous silica enhances the catalytic activity of the esterification. The esters of C10–C18 normal acid and alcohol are obtained in high yield by supported ZrOCl2·8H2O on MCM-41 although the yield of the esters decreases with the chain length of acids and alcohols. The esterification of less reactive branched acids and secondary alcohols gives excellent to good yield of the corresponding esters over supported catalysts. Zirconium cation cluster [Zr4(OH)8(H2O)16]8+ is suggested as the catalytic active species. The enhancement of catalytic performance by supporting on MCM-41 is due to increased contact between substrate and catalyst because the cation cluster is highly dispersed over MCM-41 with high surface area. The hydrophobic properties of mesoporous silica accelerate the removal of water during the esterification by controlling hydrated water in the cluster. The catalyst is recyclable without significant loss of activity.