High Toluene Conversion Research Articles

Acidity and catalyst performance of two shape-selective HZSM-5 catalysts for alkylation of toluene with methanol

Two shape-selective HZSM-5 catalysts with similar pore size were prepared by silicalite-1 coating or boron modification, respectively. These catalysts samples were characterized by XRD, SEM, NH3-TPD, Py-IR and N2 adsorption–desorption isotherms and tested in the alkylation reaction of toluene with methanol. The results indicated that the boron modification weakened the acidity but increased the total amount of acidity sites, while the silicalite-1 coating led to the decrease of the strong acidity and total acidity. Due to the specific shape-selectivity that the micropore architecture afforded and the increment of the weak acid percentage, both catalysts exhibited a high p-xylene selectivity over 98%. Moreover, the higher toluene conversion would be retained once the strong acid sites in the micropores were remained as many as possible under the premise of the shape-selectivity of pore size.

Oxygen vacancies mediated charge separation and collection in Pt/WO3 nanosheets for enhanced photocatalytic performance

Solar heterogeneous photocatalysis is a highly desirable way for the degradation of volatile organic compounds. Controlled creation of intrinsic oxygen vacancies can significantly modulate the optical and electronic properties of metal oxide semiconductors. However, poor charge utilization in defective metal oxides restrains their photocatalysis efficiency by the sluggish interfacial reaction dynamics. Herein, we demonstrate an effective photogenerated carriers collection for VOCs oxidation by mean of broadband light absorption and unidirectional electron flow to surface reactive sites by synergetic contribution of Pt nanoparticles acting as electron trapping and WO3 with abundant oxygen vacancies via facile one-step room-temperature NaBH4 treatment strategy. The optimized Vo-rich (oxygen vacancies-rich) Pt/WO3 nanosheets is able to achieve effective charge carrier utilization in a high toluene conversion of 98% even at a high CO2 yield of 95% with a quantum efficiency of 55.7% and good stability under solar light irradiation. This work highlights using oxygen vacancies-rich semiconductor as a promising support to design efficient and durable photocatalyst with collaborative optimizing charge separation and utilization, which will provide valuable insights on the defect engineering for photoredox catalysis applications toward efficient solar-to-chemical energy conversion.

Coupled Plasma-Catalytic System with Rang 19pr Catalyst for Conversion of Tar

A coupled plasma-catalytic system (CPCS) for the conversion of toluene was investigated and compared to the homogeneous system of gliding discharge plasma. Toluene was used as a model compound, which is present in tars. The study was carried out at atmospheric pressure, in a gas composition similar to the one obtained during pyrolysis of biomass. The effect of the initial toluene concentration, energy supplied to gliding discharge (GD) and the presence of a catalyst on the conversion of toluene was studied. Both the composition of outlet gas and its calorific value were monitored. Based on the obtained results it can be concluded that the conversion of toluene increases with the increase of gliding discharge power. The highest toluene conversion (89%) was received in the coupled plasma-catalytic system (catalyst: RANG-19PR) under the following conditions: CO (0.13 mol. fr.), CO2 (0.12 mol. fr.), H2 (0.25 mol. fr.), N2 (0.50 mol. fr.) and 4400 ppm of toluene with a gas flow rate of 1000 Nl/h. The composition of the outlet gas in the homogeneous system and in the CPCS changed in the range of a few percents. Toluene levels were reduced tenfold. Benzene, C3 and C4 hydrocarbons, as well as acetylene, ethylene and ethane, were detected in the outlet stream in trace amounts. Carbon deposits were present in the reactor. The products of methanation of carbon oxides were detected in the both studied systems. A mechanism of toluene decomposition in the CPCS was proposed. The application of the catalyst brought about an increase in the calorific value of the outlet gas. It was above the minimal level demanded by engines and turbines.

Catalytic Steam Reforming of Toluene for Hydrogen Production over Nickel-Cobalt Supported Activated Carbon

Hydrogen may play a key role in future sustainable energy system as a carrier of renewable energy to replace the conventional fossil fuel. Biomass gasification is the most promising method in renewable hydrogen production technologies. However, the tar by-product poses great obstacle in the realization of commercial biomass gasification. In this work, the performance of Ni and/or Co supported on modified-palm kernel shell-derived activated carbon (AC) catalyst in steam reforming of toluene (SRT) for the production of hydrogen has been investigated. Toluene has been chosen as a model compound since it represents one of the major tar compositions. The effects of nitric acid in the surface pretreatment of AC (ACN) and the influence of Ni and/or Co loading on the catalyst support are studied. The catalysts are characterized using FTIR, BET, XRD, TGA and FESEM-EDX. The modified-AC support shows that the surface area, microporous structure and surface oxygenated functional group (SOFG) increase, leading to a homogeneous distribution of metal particles. The highest toluene conversion (Xtoluene) and hydrogen yield (YH2) obtained over 10%Ni-10%Co/ACN are 70% and 69%, respectively. The catalytic performance of bimetallic Ni–Co/ACN catalyst is more significant compared to monometallic Ni- and Co-supported catalysts. The highest catalytic performance achieved can be attributed to the larger surface area and unique porous structure of the modified-AC support as well as the formation of Ni–Co solid solution alloys that improve its coke-resistant capability with low carbon formation during SRT. The modified palm kernel shell AC-supported bimetal catalyst has high potential as a biomass-based catalyst for the applications in biomass tar removal toward hydrogen production due to its good coke-resistance properties.

Plasma reforming of toluene as a model tar compound from biomass gasification: effect of CO2 and steam

In this study, plasma reforming of toluene as a tar model compound from biomass gasification has been carried out using an AC gliding arc discharge reactor. The influence of steam and CO2 addition on the reforming of toluene has been evaluated. The results show that the highest toluene conversion (59.9%) was achieved when adding 3 vol% CO2 at a toluene concentration of 16.1 g/Nm3 and a specific energy input of 0.25 kWh/m3. Further increasing CO2 concentration to 12 vol% decreased the conversion of toluene. The presence of steam in the plasma CO2 reforming of toluene creates oxidative OH radicals which contribute to the enhanced conversion of toluene and energy efficiency of the plasma reforming process through stepwise oxidation of toluene and reaction intermediates. Hydrogen and C2H2 were identified as the major gas products in the plasma reforming of toluene without CO2 or steam, with a yield of 9.7% and 14.5%, respectively, while syngas was the primary products with a maximum yield of 58.3% (27.5% for H2 and 30.8% for CO) in the plasma reforming with the addition of 12 vol% CO2. The plausible reaction pathways and mechanism in the plasma reforming of toluene have been proposed through the combination of the analysis of gas and condensed products and spectroscopic diagnostics.

Ni-doped γ-Al2O3 as secondary catalyst for bio-syngas purification: influence of Ni loading, catalyst preparation, and gas composition on catalytic activity

In this work, Ni/γ-Al2O3 catalysts were prepared by sol-gel methods with different Ni loadings (10–50 wt.%) and used as secondary catalyst for the steam reforming of toluene. A sample prepared by wet impregnation with 10 wt.% of Ni was also synthesized and compared with the corresponding sol-gel sample. This study was divided in three main parts: the comparison of catalysts prepared by sol-gel process and impregnation, the influence of the gas composition on the catalytic performance of the sol-gel 10 wt.% Ni/γ-Al2O3 catalyst, and the influence of Ni loading on the catalytic activity. When sol-gel and impregnated samples are compared, the impregnated catalyst showed a high initial toluene conversion followed by a consequent and progressive deactivation. Contrarily, the sol-gel catalyst showed a stable catalytic activity and relatively low carbon deposit. Indeed, before the steam reforming of toluene at 650 °C, the sol-gel catalyst was only calcined and no reduction step was realized to reduce nickel oxide. So this sample was reduced during the catalytic test at 650 °C. Moreover, it was observed that if toluene was withdrawn from the syngas mixture during the catalytic test, the sol-gel sample was progressively reoxidized by CO2 and H2O, leading to higher deactivation. As the Ni loading increased, the nickel oxide with strong interactions (NiAl2O4) was progressively joined by nickel oxide with low interactions (NiO/Al2O3) and bulk nickel oxide (NiO). This led to a high initial conversion of toluene but also to a progressive loss of the catalytic activity throughout the catalytic test. It was shown that the sol-gel method developed throughout this work allowed preparing microporous/mesoporous Ni/γ-Al2O3 catalysts with a high dispersion of Ni nanoparticles.

Novel approach towards Al-rich AFI for catalytic application

A new germanosilicate structural analogue of AFI zeolite (Ge-AFI) was hydrothermally synthesized. One- and two-step alumination of the Ge-AFI zeolites were used to modify their structure and acidic properties traced using XRD, N2 adsorption, ICP-OES, 27Al NMR, and FTIR spectroscopy. Two-step aluminated sample (deGe-Al-AFI) provided a higher Al content, stronger acid sites and a higher micropore volume than one-step aluminated sample (Al-AFI). Extensive evaluation of the catalytic performance of these AFI zeolites compared with reference conventional zeolite catalysts for alkylation of toluene with isopropyl alcohol showed that deGe-Al-AFI exhibited relatively high toluene conversion and selectivity to valuable p-cymene due to the optimized textural and acidic properties.

Steam reforming of aromatic hydrocarbon at low temperature in electric field

Toluene steam reforming was conducted over Ni-supported La0.7Sr0.3AlO3-δ (LSAO) perovskite oxide at 473 K in an electric field, and high toluene conversion was achieved even at such low temperature. Steam reforming is generally done at higher temperatures because of the endothermic nature of this reaction and coke prevention, which requires the contribution of heat energy in great amounts. Reportedly, water activation is particularly difficult to achieve at lower temperatures. Results of kinetic analyses such as Arrhenius plots and partial pressure dependence have revealed that imposing an electric field promotes water activation over Ni/LSAO catalyst. According to steady state isotopic kinetic analysis (SSITKA) and temperature programmed desorption infrared (TPD-IR) measurements, such water activation was accelerated via a redox mechanism using surface lattice oxygen of LSAO. The stimulated mobile lattice oxygen oxidized the adsorbed toluene and formed coke precursor in the electric field. The electric field achieved a lowered reaction temperature for efficient hydrogen production and coke suppression with redox property of LSAO support during toluene steam reforming.

Framework-Substituted Sn-MOR Zeolite Prepared by Multiple pH-Adjusting Сo-Hydrolysis As Efficient Catalyst for tert-Butylation of Toluene

A series of Sn-MOR samples with different tin species loadings were prepared via a mutiple pH‑adjusting co-hydrolysis method. Their properties were characterized by XRD, XRF, UV–Vis, FT-IR, Py-IR, N2 sorption and SEM techniques. The catalytic performance was evaluated in liquid-phase toluene alkylation with tert-butyl alcohol. The characterization results shows that compared to framework destruction of mordenite for the Sn/MOR sample with floccule prepared by ion exchange method, higher relative crystallinity and larger surface area and pore volume for Sn-MOR samples with walnut morphology can be obtained. The doping with tin species can increase the Lewis acidity and decrease the pore size resulting in both higher toluene conversion and p-tert-butyltoluene (PTBT) selectivity. The Sn-MOR(0.010) sample shows the highest catalytic performance with toluene conversion of 48.0% and PTBT selectivity of 85.6%. It shows high stability: toluene conversion of 45.3% and PTBT selectivity of 87.2% can be obtained even after 5 consecutive runs.

The synergistic effect of benzyl benzoate on the selective oxidation of toluene to benzaldehyde

To resolve the defects of acetic acid solvents for the liquid-phase oxidation of toluene to benzaldehyde with oxygen, a low-corrosive and green method was developed by introducing benzyl benzoate into the reaction. It was found that compared with the case of acetic acid, benzyl benzoate showed gratifying effect on the oxidation of toluene to benzaldehyde. The reaction was more active in the initial stage of oxidation, and the generated benzaldehyde was protected from further oxidation due to the synergistic effect of benzyl benzoate along with toluene-derived products benzyl alcohol and benzyl bromide. Benzyl benzoate inhibited the esterification of benzyl alcohol, while benzyl bromide promoted the formation of benzyl alcohol. Therefore, considerable benzyl alcohol concentration could be maintained and high benzaldehyde selectivity could be achieved under high toluene conversion.

Competitive Hydrogenation of Benzene in Reformate Gasoline over Ni Supported on SiO2, SiO2–Al2O3, and Al2O3 Catalysts: Influence of Support Nature

Nickel supported on SiO2, SiO2–Al2O3, and Al2O3 catalysts have been prepared and studied for the reduction of benzene in reformate gasoline. The sol–gel method was used to prepare the catalysts. The evaluations were performed in a continuous fixed bed micro reactor fed by a flow of reformate gasoline at 398–473 K under atmospheric pressure. The physicochemical properties of the catalysts were obtained by XRD, FESEM, EDS-map, H2–adsorption, and N2 adsorption/desorption analysis to correlate the catalytic performances. To evaluate the performance of catalysts, different H2/benzene molar ratios and space velocities were used. The Ni/SiO2-b, Ni/SiO2-c, and Ni/FDU12 catalysts decreased the benzene content to less than 1 vol % at 423 K. The high toluene conversion by Ni/MSA and Ni/Mil-53(Al) catalysts in comparison to other catalysts indicates that toluene hydrogenation is favored on these catalysts. The highest conversion of benzene in competitive hydrogenation was achieved at 423 K by the Ni/SiO2-c catalyst. ...

Low temperature removal of toluene over Ag/CeO2/Al2O3 nanocatalyst in an atmospheric plasma catalytic system

The efficient removal of toluene by plasma catalytic system (PCS) requires catalysts that can generate strong synergetic effect with discharge to oxidize toluene while promoting CO2 selectivity and suppressing the formation of harmful byproducts. We report that application of an Ag/CeO2/Al2O3 catalyst into PCS enables high conversion of toluene to CO2 and H2O with the low concentration of ozone and nitrogen oxides. The Ag nanoparticles dispersed on CeO2 surface transforms the filamentary discharge to a relatively uniform discharge with high‐efficiency, facilitates surface oxygen activation and organic intermediates oxidation, thus, enhances toluene removal efficiency. At 1800 J L−1, toluene conversion and CO2 selectivity reached maximum at 93% and 71%, respectively, whereas the removal process exhibited a good stability during a 5‐h test.

Chemical looping reforming of toluene as a biomass tar model compound over two types of oxygen carriers: 2CuO-2NiO/Al2O3 and CaFe2O4

Chemical looping reforming/gasification of toluene, the model compound representing biomass tar, was studied by using two oxygen carriers, 2CuO-2NiO/Al2O3 (molar ratio) and CaFe2O4. Their reaction performances were evaluated in a TG-FTIR and a laboratory-scale fixed bed reactor. The active lattice oxygen of the 2CuO-2NiO/Al2O3 oxygen carrier demonstrated excellent reactivity and completely oxidized toluene to CO2 at 600–700 °C, while the fixed bed reactor data indicated that 2CuO-2NiO/Al2O3 oxygen carrier could catalyze the cracking of toluene to produce H2 after loss of lattice oxygen. The CaFe2O4 oxygen carrier exhibited a good performance of chemical looping partial oxidation of toluene to CO and H2 with a fairly high reactivity. Over CaFe2O4 oxygen carrier, the CO and H2 dominated reaction products in the temperature range of 800–900 °C except at the startup stage. Catalytic cracking of toluene by CaFe2O4 to produce H2 was also observed after partial loss of lattice oxygen. Stable performance of CaFe2O4 with high reactivity to syngas (CO and H2) was demonstrated during a 3-cyle test in the fixed bed reactor. After reduction of action with toluene, scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicated that 2CuO-2NiO/Al2O3 was reduced to metallic copper and nickel with the mixture of NiAl2O4, and CaFe2O4 was reduced to metallic iron and CaO. In summary, two oxygen carriers displayed high toluene conversion at the beginning stage and the conversion of toluene increased to about 100% in the subsequent stage.

Fluidizable NiO–Fe 2 O 3 /SiO 2 –γAl 2 O 3 for tar (toluene) conversion in biomass gasification

Abstract This communication reports synergetic effects of bimetallic Ni–Fe on NiO–Fe2O3/SiO2–γAl2O3 catalysts for biomass tar (toluene) conversion. The catalysts were successfully synthesized using a one-pot, solvent-deficient method and characterized using XRD, N2 adsorption isotherm and NH3-TPD techniques. The introduction of SiO2 enhanced thermal stability of the NiO–Fe2O3/SiO2–γAl2O3 catalysts, as observed in XRD and BET surface area analysis. The synthesized NiO–Fe2O3/SiO2–γAl2O3 catalysts showed high BET specific surface area (52–58 m2/g) even after calcination at 950 °C. The NH3-TPD analysis exhibited that the addition of NiO significantly decreased the strong acid sites of the NiO–Fe2O3/SiO2–γAl2O3 catalysts. The performance of the synthesized catalysts were evaluated in a fluidized CREC Riser Simulator using toluene as a tar model compound. The NiO containing NiO–Fe2O3/SiO2–γAl2O3 catalyst yielded high toluene conversion with higher H2 concentration in the produced gas, as compared to Fe2O3/SiO2–γAl2O3 catalyst. The presence of nickel promoted both methane reforming and water-gas shift reactions, contributed to higher H2 concentration in the producer gas. A gasification process model, as developed in Aspen Plus, also showed that hydrogen composition of the producer gas can also be enhanced by adjusting the gasification temperature, pressure and steam/biomass ratios. These results indicate that the NiO–Fe2O3/SiO2–γAl2O3 catalyst has a great potential for industrial use since it is a relatively cheap, less toxic, and stable for extended period of gasification operation. The spent catalyst materials are also useful to produce other commercial products, such as Portland cement and glass-ceramics.

Green synthesis of Ni supported hematite catalysts for syngas production from catalytic cracking of toluene as a model compound of biomass tar

In this work, natural limonite (NL) was selected as the precursor of hematite (H) to prepare the Ni-based catalysts (Nix/H) for catalytic cracking of toluene. The influences of nickel loading and reaction temperature on catalytic cracking of toluene as well as the lifetime of catalyst were evaluated and the gas products were determined. The catalysts before and after catalytic cracking were characterized by XRD (X-ray diffraction), H2-TPR (H2 temperature-programmed reduction), TEM (Transmission electron microscopy), XPS (X-ray photoelectron spectroscopy). The results showed that the catalytic activity of Nix/H was obviously improved after the Ni addition due to the formation of Ni-Fe alloy. Toluene conversion increased at first with increasing of Ni loading from 0 to 6% and then decreased from 6 to 10%. High toluene conversion of 96% and stability were achieved as the Ni loading was 6% at the reaction temperature of 800 °C. Meanwhile, toluene was mainly decomposed into CO, H2, CH4, CO2 and hematite was transformed into magnetite due to the consumption of active lattice oxygen during the catalytic cracking reaction. However, the decrease in catalytic activity of Nix/H with the increase of reaction time should be attributed to the metal carbide type coke formation.

Chromium-based metal-organic framework MIL-101 as a highly effective catalyst in plasma for toluene removal

Catalytic performance of MIL-101—a type of chromium-based metal-organic frameworks (MOFs)—in a plasma catalysis system for toluene removal was experimentally studied. The MIL-101 was synthesized using a hydrothermal method, and its catalytic performance was compared to two other catalysts, Cr2O3/γ-Al2O3 and γ-Al2O3, in a dielectric barrier discharge (DBD) reactor. Results showed that the presence of a catalyst in plasma changed the voltage and current characteristic substantially, and promoted the performance of the plasma reactor. Among the catalysts, the MIL-101 exhibited a significantly high toluene conversion, which was 20% and 35% higher than Cr2O3/γ-Al2O3 and γ-Al2O3, respectively, under the same testing conditions, as well as higher carbon balance and CO2 selectivity. The analysis of by-products on the surfaces of the catalysts before and after reaction demonstrated that MIL-101 had better resistance towards by-products accumulation compared to Cr2O3/γ-Al2O3 and γ-Al2O3. The loading of MnOx on MIL-101 further promoted its catalytic performance. MIL-101 exhibits attractive catalytic properties as a catalyst in a plasma catalysis system for the decomposition of volatile organic compounds.

High utilization of methanol in toluene methylation using MFI zeolite nanosponge catalyst

A highly mesoporous MFI zeolite nanosponge, which was composed of a disordered assembly of 2.5-nm thick zeolite frameworks, was synthesized using a meso- and micropore dual structure-directing surfactant. The zeolite nanosponge was investigated as a catalyst for toluene methylation by methanol. The results showed remarkably high toluene conversion and xylene yield, in comparison with the bulk zeolite counterparts. The high catalytic performance was attributed to the suppression of side reactions that could convert methanol to linear hydrocarbons. This suppression can be attributed to the fact that the dealkylation of polymethylbenzenes, which must take place before linear hydrocarbon formation, did not occur significantly in the zeolite nanosponge as compared to the case of bulk zeolites. In addition to the aforementioned high performance, the MFI zeolite nanosponge was also superior to the bulk MFI in terms of catalytic longevity.

P-Xylene selectivity enhancement in methanol toluene alkylation by separation of catalysis function and shape-selective function

Catalyst reactivity and selectivity always compromise with each other in most reactions. HZSM-5 catalyst for the methanol toluene alkylation reaction suffers from active site loss when modified by elements such as Si, P, Mg and B to attain high p-xylene selectivity, incurring problems of low toluene conversion and rapid catalyst deactivation. In the present study, the separation of catalysis function and shape-selective function was achieved by epitaxial growing a Silicate-1 layer over HZSM-5 crystal to create an HZSM-5@S-1 catalyst. HZSM-5@S-1 was shown to possess less weak acid sites but more strong acid sites than the parent HZSM-5. With reduced contact time, the catalyst showed increased p-xylene selectivity up to 88% but no obvious degradation in toluene conversion. The enhancement of Silicate-1 shell to PX selectivity was less effective when applied to low Si/Al ratio ZSM-5 samples, due to the re-incorporation of aluminium leached from low Si/Al ratio parental ZSM-5 samples into the newly formed Silicate-1 framework. Benefiting from retaining most of the strong acid sites of HZSM-5, the catalyst showed high toluene conversion with increasing WHSV without apparent deactivation over a 130hours service life test.

Steam reforming of toluene as biomass tar model compound in a gliding arc discharge reactor

Non-thermal plasma is considered a promising and attractive approach for the removal of tars from biomass gasification to deliver a clean and high quality syngas (a mixture of H2 and CO). In this study, an AC gliding arc discharge (GAD) reactor has been developed for the conversion of toluene as a tar model compound using nitrogen as a carrier gas. The presence of steam in the plasma reaction produces OH radicals which open a new reaction route for the conversion of toluene through a stepwise oxidation of toluene and intermediates, resulting in a significant enhancement in both the conversion of toluene and the energy efficiency of the plasma process. The effects of steam-to-carbon (S/C) molar ratio, toluene feed rate and specific energy input (SEI) on the performance of the plasma steam reforming of toluene have been investigated. The optimal S/C molar ratio was found to be between 2 and 3 for high toluene conversion and energy efficiency. The maximum toluene conversion of 51.8% was achieved at an optimal S/C molar ratio of 2, a toluene feed flow rate of 4.8ml/h and a SEI of 0.3kWh/m3, while the energy efficiency of the plasma process reached a maximum (∼46.3g/kWh) at a toluene feed flow rate of 9.6ml/h and a SEI of 0.19kWh/m3. H2, CO and C2H2 were identified as the major gas products with a maximum syngas yield of 73.9% (34.9% for H2 and 39% for CO). Optical emission spectroscopy (OES) has been used to understand the role of steam on the formation of reactive species in the plasma conversion of toluene. The possible reaction pathways in the plasma conversion of toluene have also been proposed by combined means of the analysis of gas and liquid samples and OES diagnostics.

Continuous Hydrogenation of Toluene over Sr‐ and PEG800‐Modified Ni/γ‐Al2O3 Catalysts

AbstractA series of γ‐Al2O3‐supported nickel‐based catalysts were evaluated in continuous hydrogenation of toluene. Sr‐ and poly(ethylene glycol) 800 (PEG800)‐modified Ni/γ‐Al2O3 catalysts provided the best activity with high conversion of toluene and selectivity for methylcyclohexane which was ascribed to the addition of Sr and PEG800 during the preparation process, resulting in smaller and highly dispersed Ni species on the surface and in the pores of γ‐Al2O3. Furthermore, the formation of SrCO3 and NiAl2O4 is believed to be advantageous for the dispersion and stabilization of the active Ni species, accounting for its good stability.