Moderate Acid Strength Research Articles

Synthesis of bimetallic Ni-Pt/SAPO-11 composite and the catalytic application in n-heptane hydroisomerization

The monometallic Pt/SAPO-11 and bimetallic Ni-Pt/SAPO-11 catalysts were synthesized with Instant Exactness Synthesis (IES) method and characterized by XRD, nitrogen adsorption–desorption, SEM, TEM, FT-IR, Py-IR, NH3-TPD and XPS, and their properties were evaluated for the n-heptane hydroisomerization. The catalysts had spherical structure and moderate acid strength, and exhibited good n-heptane conversion and catalytic selectivity toward n-heptane isomers. Typically, Ni-Pt/SAPO-11 exhibited an isomer selectivity of 80.9% with a conversion of 69.9% at 310 °C, which was obviously better than Pt/SAPO-11 (isomer selectivity of 75.1% with a conversion of 60.6% at 310 °C). Moreover, the Ni-Pt/SAPO-11 catalyst displayed higher percentage of i-heptane (79%) and lower percentage of n-heptane (6%) than Pt/SAPO-11. The continuous test of 360 min indicated Ni-Pt/SAPO-11 catalyst had good catalytic stability. Bimetallic Ni-Pt alloy loaded on SAPO-11 had significantly effect on catalytic properties of n-heptane hydroisomerization.

CO2-assisted propane dehydrogenation to aromatics over copper modified Ga-MFI catalysts

The acidity and Ga-species status in the zeolite play a crucial role in the CO2-assisted propane dehydroaromatization (CO2-PDA). In this work, a copper modified Ga-MFI zeolite (Cu/Ga-MFI) with well dispersed framework Ga species was fabricated. A remarkable aromatics selectivity of 73% at propane conversion of 93.6% was achieved on Cu/Ga-MFI catalyst. The Ga atoms in MFI framework can create a moderate acid strength, while the introduced Cu provide an appropriate Brønsted/Lewis acid distribution, enhancing the synergy between metal-related species and the zeolite. Besides, DFT results indicate that the acid sites in Ga-MFI are more preferable for the dehydrogenation of propane instead of the C-C cleavage. Moreover, CO2 can inhibit coke formation through reverse Boudouard and reverse water gas shift reaction, which endows Cu/Ga-MFI catalyst with superior anti-coking ability and regeneration stability. This work provides a novel approach for designing catalysts with high activity, aromatics selectivity, and stability for CO2-PDA reactions.

Production of jet fuel range hydrocarbons using a magnetic Ni–Fe/SAPO-11 catalyst for solvent-free hydrodeoxygenation of jatropha oil

A novel, multifunctional Nix–Fe/SAPO-11 catalyst was synthesized and characterized, and its activity was evaluated for the solvent-free hydrodeoxygenation of jatropha oil. The catalyst has a spherical structure and moderate acid strength, and exhibited excellent cyclization and deoxidation activity. The inclusion of iron facilitated the dispersion of active components. Consequently, the iron-nickel alloy particle size remained small, resulting in an optimal distribution of the product. The composition of the products is linear alkanes (59.83%), isoparaffins (4.16%), aromatics (8.41%), and naphthenes (12.03%), where jet fuel components are relatively high, accounting for 55.04% of C8–C16 hydrocarbons. Interestingly, the iron present in the catalyst allowed the use of an external magnetic field for the rapid separation and recycling of the catalyst. Despite multiple uses, the recycled catalyst maintained high activity following five cycles, with hydrocarbon content consistently above 85%. The synergic effect of the metallic and acid sites of the catalyst, let to realize one-pot hydrodeoxygenation, isomerization, aromatization, and cracking of substrate forming bio-jet fuel range hydrocarbons.

Probing the formation of soluble humins in catalytic dehydration of fructose to 5-hydroxymethylfurfural over HZSM-5 catalyst

Understanding the formation paths of humins and corresponding influencing factors in fructose dehydration catalyzed by a solid acid would be helpful for the rational design of heterogeneous catalysts for efficient synthesis of 5-hydroxymethylfurfural (HMF). In this work, the fructose-to-HMF dehydration has been studied over HZMS-5 with various Si/Al ratios to get insights into the evolution pathways of soluble humins (i.e., oligomeric products). It was found that three main representative paths were involved in the formation of soluble humins under the catalysis of HZMS-5 solid acids: 1) oligomer I formed through dehydrated condensation of fructose and/or HMF, 2) oligomer II formed through degradative (-FA) condensation of fructose and/or HMF, and 3) oligomer III formed from degradative (–HCHO) condensation of fructose and/or HMF. We demonstrated that the Brønsted acids with weak (i.e., Alpair) and medium-strong (i.e., Alpair) strengths on HZSM-5 along with those dissolved from Lewis acidic sites (i.e., Alsingle and Alq3) both contributed to the formation of oligomer I, the medium-strong Brønsted acids and strong Lewis acids on HZSM-5 were responsible for the formation of oligomer II, and the Brønsted acids with high acid density promoted the formation of oligomer III. HZSM-5 with a low density ratio between medium-strong and weak Brønsted acids (Dmedium-strong/Dweak = 0.74) along with a low density of strong Lewis acids was found to be effective for fructose-to-HMF dehydration by inhibiting humin formations to the maximum extent. This work highlighted the rational design of heterogeneous catalysts with moderate acid density and acid strength to comprehensively avoid the formation of undesired humins in HMF biorefinery.

Highly dispersed Pd anchored on heteropolyacid modified ZrO2 for high efficient hydrodeoxygenation of lignin-derivatives

Production of biofuels and value-added chemicals from renewable biomass is a strategy with great promise to replace petrochemicals. Herein, we developed an efficient method to fabricate highly dispersed Pd anchoring on phosphotungstic acid (PTA)-modified ZrO2. The optimized metal–acid bifunctional catalyst, Pd-PTA/ZrO2, displayed excellent catalytic performance for the hydrodeoxygenation of lignin-derivatives under mild conditions. High conversion of vanillin and high selectivity of 2-methoxy-4-methylphenol can be achieved at 80 °C for 90 min under 1 atm H2, which overcame most of the reported catalysts. The outstanding catalytic activity can be attributed to the large surface area, moderate acid strength, the synergetic effect of the active metal and ZrO2 support. This study provides a feasible route to prepare highly dispersed catalysts with superior catalytic performance for bio-fuel upgrading.

Effect of Lewis/Brønsted acid sites in HZSM−5 zeolite on the selectivity of para-xylene during methylation of toluene with methanol

• The participation of Lewis acid site is good for the dissociation of methanol. • The activity of methanol dissociation has positive correlation with the acid strengths of HZSM-5 zeolites. • ZnOH + /BAS-HZSM−5 with the moderate acid strength is conducive to the formation of PX. The methylation reaction of methanol and toluene to xylenes has been carried out in Brønsted Acid Sites (BAS)−HZSM−5, AlOH 2+ /BAS−HZSM−5 and ZnOH + /BAS−HZSM−5 catalysts. The stronger acid strengths are produced in AlOH 2+ /BAS−HZSM−5 and ZnOH + /BAS−HZSM−5 due to the synergistic effect of Lewis Acid Sites (LAS) and BAS compared to BAS−HZSM−5, which is beneficial to the dissociation of methanol. AlOH 2+ /BAS−HZSM−5 shows the highest activity for methanol dissociation with the strongest acid strength. The Gibbs free energy barrier is only 68.2 kJ·mol −1 , but the formation of Para -xylene (PX) needs to overcome a high barrier of 129.2 kJ·mol −1 . However, ZnOH + /BAS−HZSM−5 exhibits relative high activity for the formation of methoxy with the Gibbs free energy barrier of 113.9 kJ·mol −1 , and 92.9 kJ·mol −1 for PX. Meanwhile, the formation of PX is easiest among three xylenes. Therefore, ZnOH + /BAS−HZSM−5 can be as the promising catalyst for the preparation of PX during methylation of toluene with methanol.

Active oxygen species and oxidation mechanism over Ce-doped LaMn0.8Ni0.2O3/hierarchical ZSM-5 in pentanal oxidation

Hierarchical ZSM-5 (HZ) molecular sieves based on fly ash were synthesized using a method combining water heat treatment with step-by-step calcination. The coupling catalysts between La1−xCexMn0.8Ni0.2O3 (x ≤ 0.5) perovskites and HZ were prepared through the impregnation method, which were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N2 adsorption, X-ray photoelectron spectroscopy (XPS), NH3-temperature programmed desoprtion (NH3-TPD), H2-temperature programmed reduction (H2-TPR) and O2-TPD techniques and investigated regarding pentanal oxidation at 120−390 °C to explore the effects of Ce doping on the catalytic activity and the active oxygen species of the coupling catalysts, meanwhile, the reaction mechanism and pathway of pentanal oxidation were also studied. The results reveal that Ce substitution at La sites can change the electronic interactions between all the elements and promote the electronic transfer among La, Ce, Ni, Mn and HZ, influencing directly the physicochemical characteristics of the catalysts. Moreover, the amount and transfer ability of surface adsorbed oxygen (O2– and O–) regarded as the reactive oxygen species and the low temperature reducibility are the main influence factors in pentanal oxidation. Additionally, La0.8Ce0.2Mn0.8Ni0.2O3/HZ exhibits the best catalytic activity and deep oxidation capacity as well as a better water resistance due to its larger amount of surface adsorbed oxygen species and higher low temperature reducibility. What’s more, appropriate Ce substitution can significantly enhance the amount of O2– ions, which can distinctly enhance the catalytic activity of the catalyst, and moderate acid strength and appropriate acid amount can also facilitate the improvement of the pentanal oxidation activity. It is found that there is a synergic catalytic effect between surface acidity and redox ability of the catalyst. According to the in situ DRIFTS and GC/MS analyses, pentanal can be oxidized gradually to CO2 and H2O by the surface oxygen species with the form of adsorption in air following the Langmuir–Hinshelwood (L-H) reaction mechanism. Two reaction pathways for the pentanal oxidation process are proposed, and the conversion of the formates to carbonates may be one of the main rate-determining steps.

The Effect of Ni-ZSM-5 Catalysts on Catalytic Pyrolysis and Hydro-Pyrolysis of Biomass.

With the demand of energy and re-utilization of wastes, the renewable lignocellulosic biomass, has attracted increasing and significant attention for alleviating the growing energy crisis and environment problems. As main components of lignocellulosic biomass, lignin, cellulose, and hemicellulose are connected by hydrogen bond to form a compact skeleton structure, resulting the trenchant condition of biomass pyrolysis. Also, pyrolysis products of above three main constituents contain a large amount of oxygenates that cause low heating value, high corrosiveness, high viscosity, and instability. Meanwhile, zeolites are of considerable significance to the conversion of lignocellulosic biomass to desirable chemical products on account of fine shape selectivity and moderate acid sites and strength. Among numerous zeolites, ZSM-5-based catalysts have been most extensively studied, and the acidity and porosity of ZSM-5 can be tuned by changing the content of Si or Al in zeolite. Beyond that, doping of other metal elements, such as Mn, Co, Ni, Ga, Ce, Pt, into ZSM-5 is also an efficient way to regulate the strength and density of acid sites in zeolite precisely. This review focused on the recent investigation of Ni-modified microporous ZSM-5 used in catalytic pyrolysis of lignin and cellulose. The application of metal-modified hierarchical ZSM-5 is also covered.

Honeycomb-structured solid acid catalysts fabricated via the swelling-induced self-assembly of acidic poly(ionic liquid)s for highly efficient hydrolysis reactions

The development of heterogeneous acid catalysts with higher activity than homogeneous acid catalysts is critical and still challenging. In this study, acidic poly(ionic liquid)s with swelling ability (SAPILs) were designed and synthesized via the free radical copolymerization of ionic liquid monomers, sodium p-styrenesulfonate, and crosslinkers, followed by acidification. The 31P nuclear magnetic resonance chemical shifts of adsorbed trimethylphosphine oxide indicated that the synthesized SAPILs presented moderate and single acid strength. The thermogravimetric analysis results in the temperature range of 300–345 °C revealed that the synthesized SAPILs were more stable than the commercial resin Amberlite IR-120(H) (245 °C). Cryogenic scanning electron microscopy testing demonstrated that SAPILs presented unique three-dimensional (3D) honeycomb structure in water, which was ascribed to the swelling-induced self-assembly of the molecules. Moreover, we used SAPILs with micron-sized honeycomb structure in water as catalysts for the hydrolysis of cyclohexyl acetate to cyclohexanol, and determined that their catalytic activity was much higher than that of homogeneous acid catalysts. The equilibrium concentrations of all reaction components inside and outside the synthesized SAPILs were quantitatively analyzed using a series of simulated reaction mixtures. Depending on the reaction mixture, the concentration of cyclohexyl acetate inside SAPIL-1 was 7.5–23.3 times higher than that outside of it, which suggested the high enrichment ability of SAPILs for cyclohexyl acetate. The excellent catalytic performance of SAPILs was attributed to their 3D honeycomb structure in water and high enrichment ability for cyclohexyl acetate, which opened up new avenues for designing highly efficient heterogeneous acid catalysts that could eventually replace conventional homogeneous acid catalysts.

Upgrading of heavy coker naphtha by means of catalytic cracking in refinery FCC unit

The upgrading of heavy coker naphtha under conditions of the industrial fluid catalytic cracking (FCC) unit has been investigated, with the aim of obtaining light olefins and a gasoline fraction suitable to be used in the blending of motor fuels. The experiments have been conducted in a riser simulator reactor at: 500 and 550 °C; catalyst to oil mass ratio, 6 gcat goil−1; and, contact time, 3 to 12 s. Moreover, the effect of the properties of two commercial equilibrium catalysts on the products has been also assessed. Products have been grouped in: dry gas, liquefied petroleum gases, gasoline, light cycle oil and coke. The presence of strong acid sites in the catalyst favors the formation of light olefins, yielding a 5 and 3.3 wt% of propylene and butenes, respectively, at 550 °C and 6 s. A higher content of zeolite (with moderate acid strength sites) and a bigger size of the mesopores of the matrix promote the formation of a commercially interesting gasoline fraction with a yield of 90 wt% under the same conditions, with a concentration of aromatics, naphthenes, n-paraffins, olefins and iso-paraffins of 25, 10, 28, 21 and 15 wt%, respectively, and a RON of 84.

Catalytic Properties of Microporous Zeolite Catalysts in Synthesis of Isosorbide from Sorbitol by Dehydration

As bisphenol A has been found to cause hormonal disturbances, the natural biomaterial isosorbide is emerging as a substitute. In this study, a method for isosorbide synthesis from sorbitol was proposed by dehydration under high temperature and high pressure reaction. Microporous zeolites and Amberlyst 35 solid acids with various acid strengths and pore characteristics were applied as catalysts. In the synthesis of isosorbide from sorbitol, the acidity of the catalyst was the main factor. MOR and MFI zeolite catalysts with high acid strength and small pore size showed low conversion of sorbitol and low yield of isosorbide. On the other hand, the conversion of sorbitol was high in BEA zeolite with moderate acid strength. Amberlyst 35 solid acid catalysts showed a relatively high conversion of sorbitol, but low yield of isosorbide. The Amberlyst 35 solid acid catalyst without micropores did not show any inhibitory effects on the production of by-products. However, in the BEA zeolite catalyst, which has a relatively large pore structure compared with the MOR and MFI zeolites, the formation of by-products was suppressed in the pores, thereby improving the yield of isosorbide.

Selective conversion of syngas to aromatics over metal oxide/HZSM-5 catalyst by matching the activity between CO hydrogenation and aromatization

Syngas conversion to aromatics has been studied over metal oxide/HZSM-5 bifunctional catalyst. In this reaction, CO is activated on metal oxide and hydrogenated to C1/C2 intermediate. The formation of aromatics involves C–C coupling, cyclization and dehydrogenation on acid sites of HZSM-5. The matching between CO hydrogenation and aromatization activity is key to the overall catalytic performance. High aromatic selectivity of up to 82.5% may be achieved over various metal oxide/HZSM-5 catalyst among which Cr2O3/HZSM-5 is the best in activity and aromatic selectivity. The CO activation and hydrogenation over Cr2O3 are facilitated by doping of Zn. The effect of Zn doping is revealed by systematic study on phase, morphology, reducibility and oxygen defect concentration. To enhance CO conversion and to prevent excessive hydrogenation, the strict control of Zn/Cr ratio and the phase of Zn species is required. The activity of HZSM-5 may be altered by changing Si/Al ratio and zeolite/oxide ratio and a moderate acid strength and density is necessary to balance the competition between aromatization and side reactions. Furthermore, the stability of the optimal catalyst 1Zn-3Cr/HZSM-5(18) is demonstrated with no significant deactivation after 100 h on stream.

Catalytic hydropyrolysis of lignin: Suppression of coke formation in mild hydrodeoxygenation of lignin-derived phenolics

Lignin, with its polyaromatic structure and as a main component of lignocellulosic biomass, is considered as an important renewable source of aromatics which are currently obtained from fossil fuels. Lignin pyrolysis gives a liquid product with a high content of phenolic compounds which can be further upgraded to aromatic hydrocarbons through catalytic approaches. In this work, in-situ catalytic hydropyrolysis combined with a subsequent ex-situ catalytic hydrodeoxygenation step was implemented to achieve an enhanced conversion of kraft lignin into aromatic hydrocarbons. The main point is that the ex-situ catalytic upgrading was conducted at mild conditions (temperature: 350 °C; pressure: 1 atm). HY was used as in-situ catalyst for enhanced decomposition of lignin. Fe/HBeta, FeReOx/MCM-41, Fe/ZrO2 and FeReOx/ZrO2 were used as ex-situ catalyst, among which the oxophilic, mesoporous and mild-acidic catalyst of FeReOx/ZrO2 revealed the highest HDO efficiency. Importantly, FeReOx/MCM-41, Fe/ZrO2 and FeReOx/ZrO2 led to significantly lower yield of coke compared to a zeolite-supported catalyst like Fe/HBeta. This suppression of coke formation is a result of reduced phenolic trapping inside catalyst mainly due to the mesoporosity and moderate acid strength of catalyst.

Studies on the catalytic activity of mesoporous alumina-aluminophosphate (Al2O3–AlPO4) materials in the synthesis of N,N′-diphenyl urea

Alumina-aluminophosphate (Al2O3–AlPO4) composite materials with various Al:P ratios were prepared at different pH and analysed for their elemental composition by AAS and ICP-AES. A few surface and bulk properties were also evaluated by PXRD, FT-IR, TPD-NH3, BET-Surface area TGA and SEM techniques. The coordination nature of Al and P in the catalysts was evaluated by MAS-NMR technique. All the materials were found to be X-ray amorphous. The materials exhibited surface acid sites with weak to moderate strength. Their surface area was in the range 218–350 m2 g−1 and were found to be mesoporous by BJH studies. Catalytic activity of the materials was investigated in synthesis of N,N′-diphenyl urea (DPU). The effect of various reaction parameters such as duration & temperature of the reaction, volume and ratio of the reactants, and the amount of the catalyst on the DPU yield was evaluated. The isolated yields of DPU in the presence of different catalysts were found to be in the range 50–80%. The catalyst with 3:1, Al:P ratio prepared at pH 8 exhibited highest catalytic activity and was found to be recyclable up to 5 times. Moderate acid strength and high surface area of the materials have been attributed to their catalytic activity in the synthesis of DPU. The role of acidity in this reaction was confirmed by poisoning the surface acidic sites using pyridine as well as by conducting the reaction with basic CaO.

Lead-containing Beta zeolites as versatile Lewis acid catalysts for the aminolysis of epoxides

Pb-Beta, a heteroatom zeolite containing out-size atoms of lead, has been successfully prepared via a scalable post-synthesis strategy composed of dealumination of H-Beta to create associated silanol and subsequent dry impregnation of the resulting Si-Beta with lead nitrate. The incorporated lead species exist in the form of well-isolated tetra-coordinated Pb2+ ions with open configurations, as revealed by the characterization results from high angle annular dark filed scanning transmission electron microscopy (HAADF-STEM), UV-Vis, X-ray photoelectron spectroscopy (XPS) and 29Si solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Sufficient Lewis acid sites with moderate acid strength are created by lead incorporation into zeolite framework, as confirmed by the temperature-programmed desorption of ammonia (NH3-TPD). The as-prepared Pb-Beta Lewis acid zeolites exhibit remarkable catalytic activity in the ring-opening aminolysis of epoxides to β-amino alcohols with high regio-selectivity. The presence of wide-open lead sites can promote the simultaneous activation of epoxide and amine substrates and, therefore, catalyze the aminolysis of epoxides with strong basic amines, e.g. butylamine.

Design of Sulphate Modified Solid Acid Catalysts for Transesterification of Diethyl Malonate with Benzyl Alcohol.

Sulphate ion modified multiwalled carbon nanotubes (S-CNTs), mesoporous carbon (S-MC), zirconia (S-ZrO2), alumina (S-Al2O3) and silica (S-SiO2) were prepared by wet impregnation technique. The physico-chemical properties of the prepared materials were investigated by Powder-XRD, BET-Surface area and SEM-EDS analysis. Surface acidity of the materials was analyzed using TPD-NH3 and n-butyl amine titration methods. Catalytic activity of these materials was investigated in liquid phase transesterification of diethyl malonate with benzyl alcohol. Effect of various reaction parameters on product yield as well as recyclability of the catalysts was investigated. Kinetics of the reactions was studied and activation energy was evaluated. All the catalysts investigated in this reaction were found to be catalytically active except S-Al2O3, for the formation of transester products; benzyl ethyl malonate (BEM) and dibenzyl malonate (DBM). S-ZrO2 and S-MC resulted good % yield (70 and 73% respectively) of total transester products where as S-CNTs showed 100% selectivity towards the formation of only BEM. Acid sites with moderate acid strength are found to be catalytically active for the transesterification reaction. The catalysts were recyclable up to 5 times without significant loss in their catalytic activity except in the case of S-MC. The reaction followed first order kinetics and the energy of activation of the reaction with different catalysts was in the range of 12-58 kJ mol-1.

Facile Formation of Lactic Acid from a Triose Sugar in Water over Niobium Oxide with a Deformed Orthorhombic Phase

Hydrothermal treatment of NH4[NbO(C2O4)2(H2O)2]·nH2O in water at 448 K for 3 days produced crystalline Nb2O5 with a deformed orthorhombic structure and a high surface area (208 m2 g–1). Fourier-transform infrared spectroscopy measurements of pyridine adsorption revealed that the Nb2O5 catalyst has both high densities of Bronsted and Lewis acid sites that can work in the presence of water. One feature of the Nb2O5 catalyst is its high density of water-compatible Lewis acid sites (0.21 mmol g–1), which is much larger than that of Nb2O5·nH2O (0.03 mmol g–1). The Nb2O5 catalyst was studied as a solid acid catalyst for the formation of lactic acid from 1,3-dihydroxyacetone and pyruvaldehyde in water at 373 K, and was determined to be a highly active and selective catalyst, compared with typical acid catalysts (H2SO4, Sc(OTf)3, and Nb2O5·nH2O). A high Lewis acid density with moderate acid strength is a crucial factor for the high catalytic performance exhibited for the former reaction. High densities of both Br...

Highly Selective Catalytic Properties of HZSM-5 Zeolite in the Synthesis of Acetyl Triethyl Citrate by the Acetylation of Triethyl Citrate with Acetic Anhydride

The catalytic activities of acid catalysts for the acetylation of triethyl citrate with acetic anhydride in the preparation of acetyl triethyl citrate were evaluated. Microporous zeolites such as HZSM-5 and HY zeolites catalysts were introduced as heterogeneous acid catalysts. HZSM-5 zeolite catalysts showed a high conversion of triethyl citrate and excellent selectivity of acetyl triethyl citrate. The catalytic activities of HZSM-5 zeolites were superior to those of the HY zeolites. In particular, the selectivity of acetyl triethyl citrate on HZSM-5 zeolites exceeded 95%. The moderate acid strength of HZSM-5 (Si/Al = 75) zeolite led to the highest catalytic activities among the HZSM-5 zeolite catalysts, which have various acid strengths.

Synergistic Effect of Mo–Fe Bimetal Oxides Promoting Catalytic Conversion of Glycerol to Allyl Alcohol

In this study, KIT-6 silica with well-ordered 3-D mesoporosity was developed as support to prepare Fe/KIT-6, Mo/KIT-6, and MoFe-x/KIT-6 (x = 0.25, 0.3, and 0.35) oxide catalysts for catalytic conversion of gas-glycerol into allyl alcohol. The catalysts were also characterized by XRD, BET, XPS, H2-TPR, and NH3-TPD. The catalytic conversion of glycerol showed a positive correlation with the surface moderate acid density of catalysts, following the order of Fe/KIT-6 < MoFe0.25/KIT-6 < MoFe0.35/KIT-6 < MoFe0.3/KIT-6 < Mo/KIT-6. Differently, the production of allyl alcohol was closely related with the moderate redox sites following a hydrogen transfer mechanism. The MoFe-x/KIT-6 showed much higher selectivity than the Fe/KIT-6 and Mo/KIT-6, which resulted from the strong synergistic effect between Fe2O3 and MoO3 altering the surface moderate acid strength, surface acid amounts, and reducibility of catalysts. The MoFe-0.3/KIT-6 exhibited a remarkable yield of 26.8% of allyl alcohol at 94.0% conversion of glycerol without external hydrogen donors supplied to the system, which benefits from the good balance between moderate acidity and weak reducibility of catalysts. The developed cubic Ia3d meso-structure was also benefit for improving the catalytic stability of MoFe0.3/KIT-6. Allyl alcohol can produce from gas–solid catalytic conversion of glycerol over the weekly acidic Fe2O3 and MoO3 supported on SiO2. The yield of allyl alcohol can be significantly improved over the MoO3–Fe2O3/SiO2 composite oxide catalysts, because of the strong interaction between MoO3 and Fe2O3. The catalytic conversion of glycerol was positively related with the surface weak acid site density of catalysts, while the allyl alcohol seems to form over the redox sites. Comparing with the single component Fe2O3/SiO2and MoO3/SiO2 catalysts, the strong synergistic effect of MoO3 with Fe2O3 guarantee the MoO3–Fe2O3/SiO2 having relatively high surface week acid site density and certain reducibility, which showed a good balance between weak acidity and reducibility thus obviously increasing the allyl alcohol yield from 26.8 to 94% catalytic conversion of glycerol through gas–solid catalytic reaction without any additives.

Activity of shaped Pt/AlSBA-15 catalysts in n-hexadecane hydroisomerization

In this study, AlSBA-15 supported Pt catalysts were tested for activity in hydroisomerization of n-hexadecane. Experiments were carried out in a continuous-flow system at 5MPa 320–360°C (WHSV=3.5h−1, H2:CH=350Nm3/m3). Shaped Pt/AlSBA-15 catalysts were prepared by two methods: (i) where the powders of AlSBA-15 materials (obtained with aluminium sulphate, aluminium nitrate or aluminium isopropoxide; Si/Al gel ratio of 20) were impregnated with H2PtCl6 solution and then shaped with binder into the extrudates and (ii) where the powders of AlSBA-15 materials (obtained with aluminium isopropoxide; Si/Al gel ratio of 20 and 7) were firstly shaped with binder into the extrudates and then impregnated with Pt precursor. The method of catalyst preparation where the binder was combined with AlSBA-15 before impregnation with the Pt precursor yielded a 1.0wt% of Pt catalyst with a comparable activity and isomerization selectivity as 1.5wt% of Pt catalyst obtained by adding the binder to the Pt/AlSBA-15 powder. The results have also revealed that the Pt catalyst with moderate acid strength, i.e. that prepared with AlSBA-15 using aluminium isopropoxide, displayed better isomerization selectivity than that one possessing strong acid sites, i.e. obtained with AlSBA-15 using aluminium sulphate; the last one displayed the highest n-C16 hydroconversion but it simultaneously provided the highest yield of hydrocracking products.