Concentration Of Strong Acid Sites Research Articles

Sustainable catalysts for esterification: Sulfonated carbon spheres from biomass waste using hydrothermal carbonization

Sulfonated catalysts derived from carbon spheres obtained from açai seeds (Euterpe oleracea) were synthesized using a hydrothermal carbonization method, followed by subsequent direct sulfonation. These solid acid catalysts, in the form of carbon spheres, were characterized through various techniques, including thermogravimetry, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy for elemental mapping (SEM-EDS), and Boehm titration. Two types of catalysts were produced through low-temperature hydrothermal carbonization. One catalyst underwent hydrothermal carbonization with the assistance of a catalyst, while the other was carbonized solely using water. The catalytic activity was assessed for up to the fifth reuse in the esterification reaction between oleic acid and methanol, employing 5% of the catalyst by mass, a 1-h reaction time at 100 °C, and a molar ratio of oleic acid to methanol at 1:12. The catalyst produced through hydrothermal carbonization in water demonstrated the best performance, with a conversion rate ranging from 91% to 88% over the five cycles, while the catalyst produced with the aid of a catalyst yielded conversion rates of 89%–82% over the same five cycles. Total acidity and sulfonic group acidity were calculated for each recycling of the aforementioned catalysts. As expected, catalytic activity was primarily influenced by the concentration of strong acid sites from the sulfonic groups, which decreased with each use of the catalyst. Scanning electron microscopy analysis confirmed that the removal of lignin from biomass residues increased the conversion of holocellulose into carbon spheres, and the functionalization with sulfuric acid did not disrupt the spherical structures of the catalysts. Thermogravimetric and differential thermogravimetric analyses showed that both hydrochars and catalysts possessed satisfactory thermal stability for use in sulfonation and esterification reactions, respectively. The TG-MS analysis allowed for the observation of the decomposition temperature of sulfur-containing gaseous emissions. FTIR and XPS confirmed the expected functional groups for hydrochars and biomass-derived catalysts. Moreover, XPS confirmed that the majority of sulfur present in the catalysts existed in the form of sulfonic groups. The optimization of reaction parameters, such as temperature, time, catalyst loading, and the molar ratio of oleic acid to methanol, was carried out using the catalyst with the best performance over the recycling cycles (91%–88%). By slightly increasing the values of these parameters in the esterification model reaction (5% catalyst by mass, 1-h reaction time at 100 °C, and a molar ratio of oleic acid to methanol of 1:12), oleic acid conversion between 89% and 93% was achieved. The utilization of açai seed-derived materials in this study showcases potential environmental benefits by reducing waste associated with açai seed commercialization. Additionally, these catalysts are considered green, as they are quick, cost-effective, and simple to produce, while exhibiting excellent catalytic activity and recyclability.

Generation of mesoporosity in crystals of zeolite omega by post-synthesis treatments with surfactants

The large-pore zeolite omega (SiAl = 3.1) has been treated with solutions of the surfactant hexadecyltrimethylammonium (CTA) in aqueous ammonia in order to generate intracrystalline mesoporosity. For this purpose, the as-made sample was calcined, transformed in the acid form by ion exchange with ammonium chloride solution followed by calcination, and the resulting acid form subsequently treated with steam at 620 ºC to partially dealuminate the framework. The samples were characterized by XRD, N2 adsorption, TGA, SEM, 29Si and 27Al MAS NMR, pyridine adsorption for acidity determination, and tested in the isomerization/disproportionation of m-xylene. It has been found that partial dealumination of the framework (Si/Al ∼ 7.3) followed by mild acid leaching (HCl = 0.3 M) to remove only the extraframework aluminium species is required for CTA to generate intracrystalline mesopores with a narrow pore diameter of 4 nm. The CTA treatment is ineffective when applied to the acid form (Si/Al ∼ 5.7) or the steamed sample before acid leaching. The concentration of strong acid sites and the average acid strength of the CTA samples are lower than those of the steamed/acid leached sample, which suggests the presence of weak acid sites located at the mesopores. The mesopores greatly enhanced the catalytic activity in the m-xylene conversion by decreasing diffusional constraints. However, the selectivity to the bulky trimethylbenzenes is not improved by the CTA treatment, which suggests that the reaction mainly takes place at the strong acid sites located at the micropores.

CO2 conversion into hydrocarbons via modified Fischer-Tropsch synthesis by using bulk iron catalysts combined with zeolites

To effectively address the challenges posed by global warming, a prompt and coordinated effort is necessary to conduct an extensive study aimed at reducing CO2 emissions and overcoming the obstacles presented by expensive and scarce fossil fuel resources. This study primarily focuses on comparing two different methodologies for preparing Na-promoted Fe3O4-based catalysts for the CO2 hydrogenation into hydrocarbon mixtures. Three catalysts were synthesized and tested: two samples were impregnated with a different amount of Na (1 wt% and 5 wt%), while a third one was obtained via coprecipitation with NaOH. As the latter catalyst exhibited the best performance, it was combined with zeolites in two ways: physical mixtures and core-shell structures. MFI-type zeolites were used in both configurations and a conventional structure was compared to a hierarchical one. As a result, mesopores increased successfully both the CO2 conversion from 37% to 40% and the liquid hydrocarbon (C6+) selectivity from 29% to 57%, doubling the C6+ yield. On the other hand, NH3-TPD and XPS measurements demonstrated that the intimate contact between the two materials in the core-shell structures led to the migration of Na from the oxide to the zeolite reducing the concentration of strong acid sites and, consequently, the liquid hydrocarbon yield.

Novel noble metal-free and recyclable Co-CoOx-FeNiCo/γ-Al2O3 catalyst for selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran or 2,5-Bis(hydroxymethyl)furan

The efficient production of the liquid fuel 2,5-dimethylfuran (DMF) from biomass-derived 5-hydroxymethylfurfural (HMF) is very complicated because of the presence of the aldehyde group, hydroxyl group, and CC bond. In this study, a novel Co-CoOx –FeNiCo/γ-Al2O3 catalyst was developed for selective hydrogenation of HMF to DMF. The catalyst was characterized by using XRD, TEM, SAED, BET, XPS, NH3-TPD, and H2-TPR techniques. The catalyst reduced at 500 °C exhibited excellent catalytic performance and the highest DMF yield (>99.9%) was obtained at 190 °C and 4 h. During the reaction, metal sites selectively hydrogenated the CO bond while acid sites (CoOx acid sites) selectively hydrogenolyzed CO bond. Appropriate surface acidity of the catalyst and the balance between metal and metal oxide species are the main factors for achieving a high yield of DMF. At reaction temperatures below 150 °C, DMF was not produced and HMF has completely converted into 2,5-Bis(hydroxymethyl)furan (BHMF), an important furan diol for polymers production. 100% BHMF yield was also obtained for the HMF hydrogenation over 300 °C reduced catalysts due to the high concentration of strong acid sites. The catalyst recyclability exhibited excellent stability and the original activity was maintained after six reuses. A reaction mechanism was also proposed.

Dispersion and Stabilization of Supported Layered Double Hydroxide-Based Nanocomposites on V-Based Catalysts for Nonoxidative Dehydrogenation of Isobutane to Isobutene

Nonoxidative dehydrogenation of isobutane is one of the sustainable strategies for producing high value added isobutene. As alternatives for the commercial Pt- and Cr-based dehydrogenation catalysts, supported V-based catalysts are worthy of study. In this work, a series of VOx/mMgAlO-R catalysts (m = 10, 15, 20, 25 and 30) were designed and prepared by loading VOx on mMgAlO composite oxide supports derived from mesoporous Al2O3-supported layered double hydroxide (LDH) nanocomposites. The calcined and reduced catalysts were characterized by X-ray diffraction (XRD), Raman spectra, Ultraviolet-visible diffuse reflectance (UV-Vis) spectra, NH3 temperature-programmed desorption (NH3-TPD), Temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TG) and low temperature N2 adsorption–desorption isotherms. The as-synthesized VOx/20MgAlO-R with appropriate Mg addition exhibits superior activity (43–56% conversion and 77–81% selectivity), excellent stability and coking-resistance for the isobutane dehydrogenation. The structure–performance relationship reveals that the formation of VOx species confined in the reconstructed LDH interlayer and porous MgO facilitates dispersing and stabilizing the VOx species. The low polymerization degree and higher proportion of V4+ ion for VOx species, strong acidity of medium acid sites and low concentration of strong acid sites are responsible for the excellent anti-coking and catalytic performance. The strong VOx–support interaction is beneficial for enhancing the stability of the catalysts.

Превращение прямогонной бензиновой фракции и газоконденсата на биметаллических ка-тализаторах на основе цеолита ZSM-5

Acidic and catalytic properties of bimetallic catalysts based on ZSM-5 zeolite modified with copper, cobalt and boron in the conversion of straight-run gasoline fraction of gas condensate were studied in a flow-through unit at atmospheric pressure, in the absence of hydrogen in the temperature range 350-4300C. It has been established that the introduction of modifiers (Cu, Co, B) into the zeolite leads to a sig-nificant decrease in the strength and concentration of acid sites. An increase in the copper concen-tration in the zeolite to 3.0 wt.% leads to a decrease in the concentration of strong acid sites from 542 to 332 mmol/g. The introduction of 2% Cu/HZSM-5 into the catalyst composition of the second modifier Co in an amount of up to 1.5 wt.% reduces the concentration of strong acid sites to 242 mmol/g. With the additional modification of the bimetallic catalyst 1.0% Co 2% Cu/HZSM-5 with boron in an amount of 0.5-1.5 wt.%, the concentration of strong acid sites further decreases to 112-198 mmol/g. On unmodified zeolite HZSM-5, which has strong acid sites, cracking and aromatization of hydro-carbons mainly take place. Isomerization of n-paraffin hydrocarbons that make up the gas conden-sate is not significant. As a result of the modification of HZSM-5 with copper in the amount of 1.0-3.0 wt. %.There is a significant increase in the catalyzate content of high-octane components: iso-paraffinic and aromatic hydrocarbons. Modification of the catalyst with 2% Cu/HZSM-5 Co in an amount of 0.5-1.0 wt.% increases its isomerizing activity, and additional modification with boron (0.5-1.5 wt.%) leads to an increase in the yield of liquid products. The relationship between the acid-ic and catalytic properties of modified catalysts has been established. The effect of increasing the isomerizing and aromatizing activity of the modified catalysts is associated with the nature, concen-tration of the modifier, and the ratio of weak and strong acid sites. The isomerizing and aromatizing activity of the catalyst is controlled by the nature and concentration of the modifier. The bimetallic catalyst 1.0% Co 2.0 Cu% 1.0% B/HZSМ-5 exhibits the highest activity in upgrading straight-run gasoline fraction of gas condensate, which makes it possible to obtain a gasoline component with an octane number of 86.5 according to IM at 3800C and a yield of 77.8 wt.%.

Methanol Dehydration to Dimethyl Ether over Modified γ-Al2O3 with Acid, Base and Zeolite (NaA and NaX)

The effect of acids, bases, zeolite NaA and zeolite NaX impregnation to g-Al2O3 on the catalyst characteristics and activity against methanol dehydration reaction were investigated. The catalyst characteristics include N2 physisorption, X-ray diffraction (XRD), and temperature-programmed desorption of ammonia (NH3-TPD) in addition to catalytic dehydration of methanol performed in a micro fixed-bed reactor at 270°C and 1 atm. The results of XRD characterization showed no changes related to the modification of alumina over acids, bases, and zeolite NaA and zeolite NaX. Therefore, the modification did not have any effect on the crystalline structure of alumina. The textural and surface acidity of g-Al2O3 changed post addition of acids, bases, zeolite NaA and zeolite NaX. NH3-TPD analysis results demonstrated that synthesized g-Al2O3 has three types of acid sites: weak, medium, and strong; however, the weak acid sites were not observed on alumina catalysts modified phosphate, KOH, zeolite NaA, and zeolite NaX. Furthermore, the concentration of strong acid sites increased in the catalyst containing KOH. The catalytic test results showed that the untreated g-Al2O3 catalyst gave prominent activity in dehydration of methanol compared to the treated catalyst following the number and strength of acid sites.

Divanadium substituted keggin [PV2W10O40] on non-reducible supports-Al2O3 and SiO2: synthesis, characterization, and catalytic properties for oxidative dehydrogenation of propane

Molecular metal oxide cluster, K5[α-1,2-PV2W10O40] (PV2W10), was found to have intrinsic catalytic activity for the oxidative dehydrogenation of propane with high selectivity (> 80%) to propylene at low propane conversion (0.3%). Synthesis of dispersed PV2W10 in non-reducible supports, γ-Al2O3 and SiO2, was done by incipient wetness impregnation. The supported catalysts were characterized by IR, Raman spectroscopy, nitrogen adsorption, x-ray powder diffraction (PXRD), elemental analysis, hydrogen temperature-programmed reduction (H2–TPR), and ammonia temperature-programmed desorption (NH3–TPD). Catalytic testing of the supported PV2W10 at equimolar cluster concentration revealed that when supported in γ-Al2O3 it is more active (sevenfold increase in propane conversion) but in SiO2 it is more selective to propylene (94%). The observed performance was due to both an increase in reducibility and higher concentration of strong acid sites for PV2W10 supported in γ-Al2O3 versus SiO2. Lastly, PV2W10 was shown to remain intact under reaction conditions indicating its thermal and oxidative stability.

The Influence of Modification on the Properties of High-Silica TsVM Zeolite in the Benzene Alkylation Reaction with Ethanol

The influence of the nature of a modifying metal (Sc, La, Gd, Yb) on the physicochemical and catalytic properties of a high-silica zeolite of the TsVM type in the alkylation reaction of benzene with ethanol has been studied in a plug-flow- reactor unit in the temperature range of 350–450°C. It has been found that the activity and selectivity of the catalyst depend on the nature of the modifying metal. The maximum yield of ethylbenzene is achieved over the Yb-loaded zeolite to be 40.7 wt % with the selectivity of 56.1%. The modified catalysts are ranked as follows with respect to the yield of ethylbenzene: Yb–HTsVM > La–HTsVM > Gd–HTsVM > Sc–TsVM. The highest ethylbenzene selectivity (59.5%) is obtained on the La-promoted zeolite. The modified catalysts are arranged as follows with respect to the ethylbenzene selectivity: La–HTsVM > Gd–HTsVM > Yb–HTsVM > Sc–HTsVM. There are substantial of amounts xylenes and di- and triethylbenzenes formed in the presence of Sc–HTsVM, leading to a decrease in the ethylbenzene selectivity. As opposed to other modifiers, the micropore volume and average pore diameter of the zeolite increase in the case of modification by Sc. It has been found that the increase in the ethylbenzene selectivity of the catalysts modified with La, Gd, and Yb is associated with the nature of the modifying metal, a decrease in the strength and concentration of strong acid sites, and a decrease in the specific surface area and total pore volume of the zeolite as a result of its chemical modification.

A Bottom-Up Strategy for the Synthesis of Highly Siliceous Faujasite-Type Zeolite.

High-silica zeolite Y is a desired catalytic material for oil refining and the petrochemical industry. However, its direct synthesis remains a symbolic challenge in the field of zeolite synthesis, with a limited improvement of the framework SiO2 /Al2 O3 ratio (SAR) from ≈5 to 9 over the past 60 years. Here, the synthesis of highly siliceous zeolite Y with tunable SAR up to 15.6 through a cooperative strategy is reported, which involves the use of FAU nuclei, a bulky organic structure-directing agent (OSDA), and a gel system with low alkalinity (named NOA-co strategy). A series of quaternary alkylammonium ions is discovered as effective OSDAs based on the NOA-co strategy, and the relevant crystallization mechanism is elucidated. Moreover, the high-silica products are demonstrated to have greatly improved (hydro)thermal stability, high concentration of strong acid sites, and uniform acid distribution, which lead to superior catalytic performance in the cracking of bulky hydrocarbons. It is anticipated that this synthetic strategy will benefit the synthesis and development of zeolitic catalysts in a wide range of reaction processes.

Monolayer MgVOx/Al2O3 catalysts for propane oxidative dehydrogenation: Insights into a role of structural, redox, and acid-base properties in catalytic performance

Here we report the relationships between the structure of the vanadia species, acid-base, and redox properties of the surface of tailor-made monolayer MgVOx/Al2O3 catalysts and the effects of these features on the performance of such catalysts. Combined Raman and UV-vis DR spectroscopies confirmed the formation of the alumina-supported 2D surface VOx and MgVOx species with different coordination and local environment of the active site. The Mg incorporation into the structure of the surface vanadia species was shown to affect both their redox and acid properties and allows controlling the catalyst activity and selectivity towards propylene. Increasing the binding energy of V–O bonds due to Mg doping was shown to be critical to improve the catalyst performance but is not the only factor determining high selectivity towards propylene that is also affected by the concentration of strong acid sites and surface species structure.

Zn-promoted Hβ zeolite for gas-phase catalyzed aza-heterocyclic-aromatization of acrolein dimethyl acetal and aniline to quinolines

Catalytic activities of Zn-promoted Hβ zeolite for gas-phase aza-heterocyclic-aromatization of acrolein dimethyl acetal and aniline to quinolines were investigated. the Zn/Hβ catalyst showed better selectivity to quinoline than the parent Hβ one. Characterization results demonstrated that the Zn/Hβ catalyst prepared via deposition precipitation method existed the isolated Zn2+ cations as well as the highly dispersed ZnO clusters, which not only decreased concentration of strong acid sites but also enhanced enhance aromatization process. As a result, the decrease of strong acid sites restrained the cracking of acrolein to acetaldehyde as well as the alkylation of quinoline to ethylquinoline effectively; and the Zn species of catalyst further improved aromatization process of dihydroquinoline to quinoline. Moreover, the Zn/Hβ catalyst presented relatively enhanced ability of anti-activation and excellent regenerability, owing to decrease strong acid-induced polymerization of active intermediates to form the coking. Under the optimized operating conditions, more than 51 % yield of quinoline was achieved over Zn/Hβ catalyst; which far exceeded quinoline yield (28 %) over the pure Hβ one. Besides, a plausible reaction routes in vapor-phase acrolein diethyl acetal with aniline to quinolines were suggested in this paper.

Catalytic pyrolysis over transition metal-modified zeolites: A comparative study between catalyst activity and deactivation

Using metal-doped zeolites in catalytic pyrolysis of biomass is a well-known approach to promote the formation of certain compounds. One of the major technical issues with such catalysts is their rapid deactivation due to coke formation. However, little is known about how metal-doping influences the characteristics of coking, such as coking rate and its composition.In this study, four different materials were experimentally evaluated based on their catalytic activity and coking characteristics: HZSM-5, Fe/ZSM-5, Ni/ZSM-5 and FeNi/ZSM-5. The materials were prepared and characterized followed by screening in a bench-scale setup for in-situ catalytic pyrolysis. The mass balance and composition of pyrolysis products including catalyst coke were analyzed.It was found that metal-doping increases the concentration of aromatic hydrocarbons in the liquid product from 59.0 to 82.8% of GC/MS peak area, especially monoaromatic hydrocarbons (MAHs) and naphthalenes. Fe mainly increases the selectivity of MAHs whereas Ni additionally promotes naphthalenes. FeNi/ZSM-5 reflects the combined effect of Fe- and Ni-doped catalysts. Regarding the catalyst coke composition, metal-doped catalysts present an increased concentration of aromatic hydrocarbons. For each catalyst, the chemical composition of the coke reflects the catalytic activity seen in vapor upgrading. Based on the findings in this work, a reaction pathway for metal-doped ZSM-5 and HZSM-5 is proposed.The results also show that metal-doping increases the formation of catalyst coke, mainly due to a higher concentration of strong acid sites. Also, the severity of coking was found to be dependent on the strength of acid sites. The coke yield increased from 3.5 wt% in the case of HZSM-5 to maximum 7.2 wt% over Fe/ZSM-5. At the same time metal-doping reduces the temperature of catalyst regeneration and catalyzes the oxidation of coke. Overall, this work presents a comparative study between catalyst activity and deactivation during thermochemical conversion of biomass.

Selective allylic oxidation of cyclohexene over a novel nanostructured CeO2–Sm2O3/SiO2 catalyst

Selective allylic oxidation of cyclohexene was investigated over nanostructured CeO2/SiO2 and CeO2–Sm2O3/SiO2 catalysts synthesized by a feasible deposition precipitation method. The CeO2–Sm2O3/SiO2 catalyst showed excellent catalytic efficiency with ~89 % cyclohexene conversion and ~90 % selectivity for allylic products (i.e., 2-cyclohexen-1-ol and 2-cyclohexene-1-one), while only ~50 and ~35 % cyclohexene conversion was observed, respectively, over CeO2/SiO2 and CeO2 catalysts. Systematic characterization of the designed catalysts was undertaken to correlate their catalytic activity with the physicochemical properties using X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) surface area measurements, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and NH3-temperature programmed desorption (TPD) techniques. The results revealed that doping of Sm3+ into the ceria lattice and simultaneous dispersion of resultant Ce–Sm mixed oxides on the silica surface led to improved structural, acidic, and catalytic properties. The better catalytic efficiency of CeO2–Sm2O3/SiO2 was due to high specific surface area, more structural defects, and high concentration of strong acid sites, stimulated by synergistic interaction between various oxides in the catalyst. The cyclohexene conversion and selectivity for allylic products depended on the reaction temperature, nature of solvent, molar ratio of cyclohexene to oxidant, and reaction time. Possible reaction pathways are proposed for selective allylic oxidation of cyclohexene towards 2-cyclohexen-1-ol and 2-cyclohexene-1-one products. SiO2-supported CeO2–Sm2O3 nanocatalyst exhibited outstanding catalytic performance with superior selectivity for allylic products in liquid-phase selective oxidation of cyclohexene under mild reaction conditions.

Selective ring opening of decalin on Rh-Pd/SiO2-Al2O3 bifunctional systems: Catalytic performance and deactivation

Ring opening of decalin was studied using Rh-Pd(x) catalysts supported on SiO2-Al2O3, prepared by coimpregnation with a variable total metallic content (x = 1, 1.5 and 2 wt%) while maintaining constant the Rh/Pd atomic ratio (equal to 1). The catalytic performances of these bimetallic systems were compared to those of monometallic Pd and Rh (1 wt%) catalysts. Bimetallic Rh-Pd(x) catalysts were unable to achieve decalin conversion and ring opening selectivity as high as those obtained using the Rh catalyst (~71 and ~67%, respectively, after 6 h reaction time). The principal cause was the reduction of the hydrogenolytic activity and acidity caused by the combination of Pd and Rh. In the case of the bimetallic Rh-Pd(x) samples, an increase in the metal content favored the formation of dehydrogenated products, reduced cracking (by reducing the concentration of strong acid sites) and increased coke deposition during decalin ring opening. Conversely, the Rh catalyst showed less deactivation since its efficient hydrogenolytic character eliminates coke precursors.

Effects of rare-earth (Nd, Er and Y) doping on catalytic performance of HZSM-5 zeolite catalysts for methyl mercaptan (CH3SH) decomposition

A series of HZSM-5 zeolite catalysts modified with various rare earth metals (Nd, Er and Y) was prepared and used for CH3SH catalytic decomposition test. The results revealed that addition of rare earth metals significantly improved activity and stability of the HZSM-5 zeolite catalysts, and Nd-modified catalyst exhibited the best performance. Several characterization studies were undertaken to correlate structural and surface properties of the obtained catalysts with their catalytic performance. It was found that acid-base properties of the catalysts were closely related to the catalytic performance. The NH3-TPD and CO2-TPD analysis showed that the concentration of strong acid sites of the HZSM-5 catalysts decreased after rare earth metals addition, while the concentration of basic sites of the catalysts increased. The decrease in the amount of strong acid sites suppressed the formation of coke on the catalysts. The catalysts with increased amount of basic sites displayed better adsorption ability to CH3SH. The UV–vis, 27Al NMR and XRD analysis indicated that the existence of an empty f orbit Nd3+ caused the increase of non-framework aluminium species amount, which leaded to the decrease of the strong acid sites amount. In addition, the optimal loading amount of Nd was investigated and 13wt%Nd/HZSM-5 catalyst showed no obvious deactivation during 60h test. The spent Nd/HZSM-5 catalyst can be successfully regenerated, showing that Nd/HZSM-5 was an efficient catalyst for CH3SH elimination.

Influence of the Preparation Method on Hybrid Catalysts CuO–ZnO–Al2O3 and H-Ferrierite for Syngas Transformation to Hydrocarbons via Methanol

Hybrid catalysts using CuO–ZnO–Al2O3 as a catalyst for the synthesis of methanol and an H-ferrierite zeolite as the dehydration component were prepared using four different methods to study the influence of the method of preparation on the active sites available on both components and the performance of the hybrid catalyst in the conversion of syngas in hydrocarbons. The samples were characterized by X-ray diffraction, N2 adsorption, temperature-programmed reduction, temperature-programmed desorption of H2, temperature-programmed desorption of ammonia, and transmission electron microscopy. The samples were tested in a tubular reactor at 2.0 MPa and 350 °C. The preparation methods influenced the interaction between both components and consequently affected the surface properties of each component. The Cu surface area and available acid sites were affected by the preparation method. The coprecipitation-sedimentation method showed a better interaction between both components, a high Cu surface area and a high concentration of strong acid sites.

Vacuum gas-oil hydrocracking performance of Beta zeolite obtained by hydrothermal synthesis using carbon nanotubes as mesoporous template

Beta zeolite was synthesized under hydrothermal conditions using multi-walled carbon nanotubes with an outer diameter of 8–15nm as a nanometric template. The textural, structural, and acidic properties were characterized by X-ray diffraction, thermogravimetric and differential thermal analyses, chemical analysis, N2 physisorption, scanning and transmission electron microscopies, 27Al solid-state nuclear magnetic resonance, and infrared spectroscopy of adsorbed pyridine. Ni–Mo hydrocracking catalysts were prepared from the calcined zeolites. Their catalytic performance was evaluated by hydrocracking heavy vacuum gas oil. Results indicated that adding carbon nanotubes to the synthesis gel produces a substantial increase of mesoporosity in the obtained Beta zeolite. This resulted in a decrease of the total Brønsted acid sites, particularly those of higher acid strength. The most active hydrocracking catalyst was the one prepared with the zeolite synthesized using carbon nanotubes. For the same conversion level, selectivity to middle distillates and naphta increased with the concentration of strong acid sites in the catalysts.

Hydrogenolysis of glycerol over HY zeolite supported Ru catalysts

An enhanced active and selective catalyst consisting of ruthenium supported on dealuminated HY zeolite has been prepared by a wet impregnation method. It was found that BET surface area of Ru/HY catalysts significantly increases after HCl treatment. This treatment also increases the concentration of strong acid sites in the catalyst. The hydrogenolysis of glycerol over 5 wt% Ru/HY catalyst was investigated at 190–220 °C, an initial H2 pressure of 3–6 MPa, and in 20 wt% glycerol aqueous solution. The results indicate that HCl treated Ru/HY catalyst shows higher activity compared with the untreated Ru/HY catalyst, and that the glycerol hydrogenolysis efficiency is influenced by the porosity and acidity of the support. A selectivity to 1,2-PDO of 81.3% at a glycerol conversion of 60.1% under 3 MPa H2 pressure and 220 °C for 10 h was achieved over the modified Ru/HY catalyst with a 1.0 mol/L HCl treatment. It has also been shown that a longer reaction time, a higher temperature and a higher H2 pressure have the positive effects on the glycerol hydrogenolysis efficiency of the enhanced Ru/HY.

Methanol-to-Olefin Conversion over Zeolite Catalysts: Active Intermediates and Deactivation

Methanol-to-olefin (MTO) conversion over various zeolites with different topologies, Si/Al molar ratios, and crystallite sizes were investigated to verify the effects of pore shape and size, acidity, and external surface area on the catalytic activity, product selectivity, and deactivation. The IR and electron spin resonance (ESR) study of zeolite catalysts used in MTO also proceeded to deduce the active intermediates formed in their cages or pores. The zeolites with 8 membered-ring (MR) pore entrances such as CHA, ERI, LTA, and UFI commonly exhibited high selectivity to lower olefins due to their small entrances, but the CHA catalyst with the smallest cage maintained its activity longer than other 8MR zeolites. The slow condensation of polymethylbenzene (PolyMB) to polyaromatic hydrocarbons (PAH) on MOR zeolite with a high Si/Al molar ratio due to its low concentration of strong acid sites resulted in a slow deactivation. The extremely small crystallites of H-SAPO-34 and H-ZSM-5 less than 100 nm showed an adverse effect in MTO; while the large crystallites above 1,000 nm also exhibited poor catalytic performance because of their small external surface. The study of IR regarding the adsorbed and occluded materials on zeolites demonstrated the effect of pore shape and size on the active intermediates: the zeolites with larger pores and cages allowed the formation of alkylbenzenes with long alkyl groups which preferred to be condensated to PAH. The well-resolved hyperfine splitting of ESR spectra observed on H-SAPO-34 used in MTO clearly illustrated the presence of hexamethylbenzenium radical cations. The small intersections of phosphorous-modified H-ZSM-5 allowed the formation of tetramethylbenzenium radical cations in MTO. The formation of PolyMB radical cations, their role as active intermediates and the effect of topology, acidity, and crystallite size of zeolites on their deactivation were discussed.