Toluene Selectivity Research Articles

One-step conversion of lignin-derived alkylphenols to light arenes by co-breaking of C–O and C–C bonds

The selectivity for light arenes, including benzene and toluene, in the conversion of 4-ethylphenol reaches 55.7% with 84.0% selectivity for arenes.

Hierarchical pore construction of alumina microrod supports for Pt catalysts toward the enhanced performance of n-heptane reforming

Regulation of pore hierarchy has been an important subject in the design of industrial catalysts. Synthesis of alumina without template/additive often results in poor control of morphologies, porosities, and metal dispersion thereafter. Herein, alumina microrods with a tailored pore hierarchy (Rod2) were fabricated without template/additive by tuning the pore structure of the synthetic precursors, which were used as supports of Pt for n-heptane reforming. Improved toluene selectivity was observed at low space velocities as a result of promoted dehydroisomerization of pentacyclic hydrocarbons, presumably due to a combined effect of the desired pore hierarchy and rod morphology. The Pt/Rod2 also showed better resistance to carbon deposition while maintaining good metal dispersion, as compared to alumina supports with spherical morphology or uncontrolled pore hierarchy. The simulation results revealed that the improved toluene selectivity of Pt/Rod2 is attributed to the proper pore combination of meso-pore1 (6–40 nm) and meso-pore 2 (40–300 nm).

Recovery of Arenes from Polyethylene Terephthalate (PET) over a Co/TiO2 Catalyst.

Upcycling of spent plastics has become a more emergent topic than ever before due to the rapid generation of plastic waste associated with the change of lifestyles of the human society. Polyethylene terephthalate (PET) is a major aromatic plastic and herein, the conversion of PET back into arenes was demonstrated in a one-pot reaction combining depolymerization and hydrodeoxygenation (HDO) over a Co/TiO2 catalyst. The effectiveness of the Co/TiO2 catalyst in HDO and the underlining reaction pathway were established using the PET monomer terephthalic acid (TPA) as the substrate. Quantitative TPA conversion together with 75.2 mol% xylene and toluene selectivity under 30 bar initial H2 pressure at 340 °C was achieved after 4 h reaction. More encouragingly, the catalyst induced both depolymerization and HDO reaction via C-O bond cleavage when PET was used as a substrate. 78.9 mol% arenes (toluene and xylene) was obtained under optimized conditions.

Ni-Cu High-Loaded Sol-Gel Catalysts for Dehydrogenation of Liquid Organic Hydrides: Insights into Structural Features and Relationship with Catalytic Activity.

The heightened interest in liquid organic hydrogen carriers encourages the development of catalysts suitable for multicycle use. To ensure high catalytic activity and selectivity, the structure–reactivity relationship must be extensively investigated. In this study, high-loaded Ni–Cu catalysts were considered for the dehydrogenation of methylcyclohexane. The highest conversion of 85% and toluene selectivity of 70% were achieved at 325 °C in a fixed-bed reactor using a catalyst with a Cu/Ni atomic ratio of 0.23. To shed light on the relationship between the structural features and catalytic performance, the catalysts were thoroughly studied using a wide range of advanced physicochemical tools. The activity and selectivity of the proposed catalysts are related to the uniformity of Cu distribution and its interaction with Ni via the formation of metallic solid solutions. The method of introduction of copper in the catalyst plays a crucial role in the effectiveness of the interaction between the two metals.

High‐flux and solvent‐selective membranes with aromatic functionalities and dual‐layer structures

AbstractEfficient separation of aromatic‐aliphatic hydrocarbon mixtures has long been an important topic in chemical industries. Organic nanofiltration (OSN) has been revealing great promise in separating solvent mixtures that has not been effectively resolved by the state‐of‐the‐art technologies. Herein, novel OSN membranes are designed for the separation of toluene and n‐heptane. Polyamide active layer with diaminonaphthalene as the aqueous phase monomer is prepared by interfacial polymerization for the first time. The addition of polydimethylsiloxane gutter layer, as well as the combination of spin coating technique and macroporous substrate, renders the membranes with loose and defect‐free architectures. The as‐designed membranes achieve a rather high selectivity of toluene over n‐heptane (>4) together with ultra‐high toluene permeance (>180 L m−2 h−1 bar−1). These membranes also present excellent stability in the long‐term operation.

The effect of indium introduction method on the properties of Pt/In/Al2O3-Cl reforming catalyst

The effect of 0.3 wt.% indium, which was introduced at the steps of alumina peptization or impregnation, on the properties of platinumalumina reforming catalysts was studied. Doping with indium at the impregnation step produced a smaller decrease in the total acidity of the support and hence in the heptane conversion for the corresponding Pt/In/Al2O3-Cl catalyst. The most pronounced decrease in selectivity of hydrogenolysis and hydrocracking and the maximum i-C5-7 : toluene selectivity ratio were observed for this sample as compared to the undoped catalysts with indium introduction at the peptization step.

Structure–Property Relationships of Pt–Sn Nanoparticles Supported on Al2O3 for the Dehydrogenation of Methylcyclohexane

The structure–catalytic property relationships of Al2O3-supported Pt–Sn nanoparticles (Pt–Sn/Al2O3) in the dehydrogenation of methylcyclohexane (MCH) were investigated by varying the Sn/Pt ratios of the catalysts. The initial activity and the deactivation rate of the Pt–Sn/Al2O3 catalysts in the MCH dehydrogenation decreased in line with an increase in the Sn/Pt ratio from 0 to 3. The Pt–Sn/Al2O3 catalyst with a Sn/Pt ratio of 2 showed good activity, durability, and toluene selectivity in the MCH dehydrogenation among the series of catalysts. The dispersion of Pt in the Pt–Sn/Al2O3 catalysts was observed to decrease with an increase in the Sn/Pt ratio. Structural changes in the catalysts from Pt–Sn clusters to intermetallic Pt3Sn and PtSn nanoparticles were also observed using scanning transmission electron microscopy and X-ray diffraction. According to structural analysis using X-ray absorption fine-structure spectroscopy and infrared spectroscopy using carbon monoxide as a probe, the electron density of Pt increased, and the fraction of Pt–Pt adjacent sites decreased with an increase in the Sn/Pt ratio. Comparing the catalytic properties and the structures of the Pt–Sn/Al2O3 catalysts, their initial activities were correlated with the dispersion of Pt. In addition, the durability and selectivity of the catalysts were enhanced due to an increase in the electron density of Pt and a decrease in the number of Pt–Pt adjacent sites. Overall, the properties of the catalysts in the MCH dehydrogenation are determined by the local structure of Pt atoms rather than the crystal structure of the Pt–Sn alloy nanoparticles on Al2O3.

Co-promoted few-layer and defect-rich MoS2 for enhanced hydrodeoxygenation of p-cresol

Unsupported CoMo sulfide catalysts are good candidates in the hydrodeoxygenation (HDO) of phenol compounds to aromatics which is important for bio-oil upgrading. However, the key to prepare efficient catalysts is how to increase the content of Co-Mo-S active phase as much as possible. Herein, a dual strategy of layer and defect engineering was realized for the synthesis of few-layer and defect-rich MoS2 (MoS2-FL-DR) through a simple one-pot hydrothermal method. By decreasing the layer number and manufacturing abundant defects on the basal planes, more coordinatively unsaturated sites (CUS) were formed to provide additional sites to accommodate Co atoms. After promoted with Co, Co/MoS2-FL-DR exhibited an excellent performance in the HDO of p-cresol, with p-cresol conversion of 100 % and toluene selectivity of 99.7 % at 230 °C. This catalyst also showed a relative good stability after reaction for 72 h. The excellent performance was attributed to the few-layer and defect-rich structure of MoS2 and the formation of large amount Co-Mo-S active phase.

Selective breaking of C−O bonds in hydrodeoxygenation of 4-methylphenol over CoMoS/ZrO2

CoMoS/ZrO2 catalysts with different Co-Mo atomic ratios (0.25, 0.30, 0.35, 0.40 and 0.45) and Co-Mo loading amounts (2.35%, 4.36%, 7.48% and 10.79%) were prepared by incipient wetness impregnation. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR), nitrogen adsorption/desorption and X-ray photoelectron spectroscopy (XPS). 4-methylphenol was used as model compound for hydrodeoxygenation reaction. The result showed that when the atomic ratio of Co-Mo (Co/Co + Mo) was 0.30 and the Mo loading amount was 4.36%, the highest hydrogenation activity was observed. The conversion of 4-methylphenol was up to 99.86% and the selectivity of main product toluene reached to 87.85%. The formation of CoMoO4 was unfavourable to the formation of toluene. An appropriate interaction between Co-Mo and ZrO2 was required.

Comparative study on the two-step and one-step pyrolysis of lignin: effects of pyrolysis temperature and residence time on the product distribution

To explore a new way of utilizing lignin and deepen the understanding of mechanism of two-step pyrolysis (TSP) of biomass, the effects of the first step pyrolysis temperature (T1) and residence time (RT1) on TSP of lignin were studied by using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). TSP of lignin was also compared with one-step pyrolysis (OSP) of lignin. The results indicated that higher pyrolysis temperature promoted the break of ether linkage among the structural elements of lignin and the removal of side chains. With T1 increasing, the contents of monophenols (MPs), catechols (CPs), monocyclic aromatic hydrocarbons (MAHs), and polycyclic aromatic hydrocarbons (PAHs) increased in the first step, while the contents of methoxyphenols with double bond in the side-chain (MPBSs) and methoxyphenols with no double bond in the side-chain (MPSs) increased firstly and then decreased. In the second step, with T1 increasing the contents of MPs and CPs increased firstly and then decreased, the contents of MAHs and PAHs increased significantly, and the contents of MPBSs and MPSs decreased. Higher T1 increased the yields of the most identified compounds of the first step, but decreased the yields of MPs, CPs, MPBSs, and MPSs in the second step. RT1 had great effects on the pyrolysis behaviors and product distribution of TSP of lignin, and the content of MAHs and PAHs in the second step increased significantly with RT1 increasing. Compared with OSP, the yields of MAHs and PAHs could increase in the second step. TSP of lignin could improve the selectivity of value-added chemicals remarkably, such as guaiacol, vanillin, acetovanillone in the first step, and the selectivity of benzene, toluene, m-xylene, phenol, o-cresol, and p-cresol in the second step.

Highly efficient unsupported Co-doped nano-MoS2 catalysts for p-cresol hydrodeoxygenation

To prepare catalyst with high activity, high selectivity and good stability remains the biggest challenge in the hydrodeoxygenation (HDO) of phenols by adopting MoS2-based sulfides as catalysts. Herein, we report a simple hydrothermal method to synthesize highly-dispersed nano-MoS2 with abundant defects and some curved slabs. All these advantages enable nano-MoS2 to provide a large number of coordination unsaturated sites to anchor Co atoms. The unsupported Co-doped catalyst with an optimal Co/(Co + Mo) molar ratio of 0.3 exhibited excellent performance in the HDO of p-cresol with conversion of 98.7 % and toluene selectivity of 98.9 % at 220 °C. Moreover, the optimized Co/MoS2-0.3 catalyst had a good stability after reaction of 72 h. The excellent HDO performance was attributed to the formation of abundant Co-Mo-S active sites which optimize the electrical structure of nano-MoS2 by Co promoter.

Separation of toluene from a toluene/n-heptane mixture using ethylene glycol containing deep eutectic solvents

Deep eutectic solvents (DESs) were synthesized and used to separate toluene from n-heptane. DES3 and DES4 were synthesized using choline chloride, urea, and ethylene glycol with a molar ratio of 1: 2: 1 and methyltriph-enylphosphonium bromide and ethylene glycol with a 1: 3 ratio, respectively. While dynamic viscosity of DES2 ranged from 575.9 to 73.8 over temperatures 293.2 to 323.2 K, respectively, that of DES3 ranged from 219.5 to 39.44 [mPa·s]. The viscosity of both DES3 and DES4 follows the Arrhenius equation with respect to temperature from 293.2 to 323.2 K. The liquid-liquid equilibrium (LLE) of the pseudoternary system of toluene, n-heptane, and DES3 were performed at temperature of 303.2 K at ambient pressure. Another LLE of the pseudoternary system of toluene, n-heptane, and DES4 were was obtained over a temperature range of 298.2–313.2 K with a 10 K interval at atmospheric pressure. The experimental LLE data were correlated using the non-random two-liquid (NRTL) model. DESs were not detected in the raffinate phase, and as a result no further separation process for DES was necessary in the toluene separation process. The values of selectivity in the presence of DES 4 changed in a range from 24.4 to 147.5, however, those in the presence of DES3 from 4.1 to 18.7 at 313.2 K. The values of selectivity of toluene with DES applied in this study were far higher than those with other conventional solvents.

Micro-mesoporous carbon fabricated by Phanerochaete chrysosporium pretreatment coupling with chemical activation: Promoting effect and toluene adsorption performance

Porous carbons prepared from biomass by the traditional method of caustic potash etching is common VOCs adsorbents, but their lack of mesopores hinders the mass transfer, limiting their application. Herein, we prepared templateless micro-mesoporous carbon with a high specific surface area by coupling Phanerochaete chrysosporium pretreatment to caustic potash etching, and explored its synergy mechanism. The prepared micro-mesoporous carbon has simultaneously high specific surface areas (2202 m2/g) and proportion of mesopores (71.9%). The promoting effect determined by FTIR and TG-MS implied that P. chrysosporium treatment increases surface oxygen-containing groups (K+ combine sites). It led to the simultaneous formation of mesopores without any template. P. chrysosporium pretreated carbonaceous materials exhibited more defects, which resulted in a high specific surface area. Moreover, the samples that were subjected to P. chrysosporium pretreatment and caustic potash etching exhibited higher adsorption capacity (252 mg/g) and higher selectivity for toluene over N2.

Alkylation of Toluene with Isopropanol on Lantanum Modified ZSM-5 Zeolite

The effect of lanthanum concentration on the physicochemical and catalytic properties of HZSM-5 zeolite in a reaction of toluene alkylation with isopropanol was studied in a temperature range of 250–350°C. Based on the data obtained by X-ray diffraction analysis, low-temperature nitrogen adsorption (BET method), and IR spectroscopy, it was shown that an increase in lanthanum concentration in HZSM-5 from 1.0 wt % to 7.0 wt % reduces both the specific surface area and the pore volume of the zeolite despite the retention of its crystalline structure. This also results in redistribution of acid sites, specifically decreases the concentration of strong Bronsted acid sites (B) and increases that of moderate Lewis acid sites (L), thus decreasing the B/L ratio from 3.53 to 0.20. All these occurrences have a crucial effect on the selectivity of reaction products and, in particular, on the p-isopropyl toluene (4-IPT) selectivity. Maximum selectivity, making up 72.4%, is achieved by a zeolite containing 5.0 wt % lanthanum at a B/L ratio of 0.25.

Simulating alveoli-inspired air pockets in a ZnO/NiMoO4/C3N4 catalyst filter for toluene entrapment and photodecomposition

Here, we propose an alveoli–inspired catalyst to address the susceptibility of photocatalytic air oxidation systems to fluctuations in volatile organic contaminant (VOC) loads. An alveoli structure was fabricated by covering ZnO nanorods grown on a stainless–steel mesh (SSM) with a porous NiMoO4/C3N4 layer. The alveoli catalyst regulates VOC mass transfer from the air to the catalyst surface using air pockets that capture VOC molecules by diffusion driven by a concentration gradient. Air pockets act as localized reservoirs of molecules that prevent scarcity and congestion at the catalyst surface at low and high VOC loads, respectively. The presence of air pockets in the catalyst assembly and its potential to capture VOC was confirmed by a distinct bimodal adsorption configuration. A ZnO/NiMoO4/C3N4@SSM (ZNC@SSM) catalyst with air pockets achieved a high degree of toluene adsorption (6.1 μmol·m–2). Toluene selectivity of ZnO controlled the delivery of molecules to active catalyst sites, resulting in 95% toluene conversion in 90 min. Synergetic toluene adsorption in air pockets and degradation on catalytic sites helped achieve a quantum yield of 4.14 × 10–05 molecules/photon. A figure of merit reflecting fundamental system parameters was compared with previous photocatalytic systems to evaluate the practicality of ZNC@SSM.

High-Loaded Nickel Based Sol–Gel Catalysts for Methylcyclohexane Dehydrogenation

Application of liquid organic hydrogen carriers, such as “methylcyclohexane (MCH)–toluene” chemical couple, is one of the promising approaches for hydrogen storage and transportation. In the present study, copper-modified nickel catalysts with high metal loading of 75 wt% were synthesized via heterophase sol–gel technique, and investigated in the dehydrogenation of MCH. Two approaches towards the copper introduction were applied. The catalyst samples prepared via wetness impregnation of the nickel sol–gel catalyst are characterized by more effective Ni-Cu interaction compared to those where two metals were introduced simultaneously by the mixing of their solid precursors. As a result, the “impregnated” catalysts revealed higher selectivity towards toluene. The addition of copper up to 30 wt% of total metal content was shown to increase significantly toluene selectivity and yield without a noticeable decrease in MCH conversion. The catalyst with the active component including 80 wt% of Ni and 20 wt% of Cu demonstrated 96% and 89% toluene selectivity at 40% and 80% MCH conversion, respectively. Based on the obtained data, this non-noble catalytic system appears quite promising for the MCH dehydrogenation.

In Situ Formation of CoMoS Interfaces for Selective Hydrodeoxygenation of p-Cresol to Toluene

Catalytic hydrodeoxygenation (HDO) of phenolics to aromatics is one of the most important reaction routes in bio-oil upgrading. Sulfided CoMo catalysts are good candidates for this reaction, but their activities are strongly associated with the number of exposed surface sites and Co–Mo synergy. Herein, we employ zeolitic imidazolate framework-67 as a cobalt precursor and template for inverse deposition of MoS2 ultrathin sheets inside the framework to form CoMoS interfaces by using a simple hydrothermal method. The size-confined MoS2 possesses a few-layered structure and abundant surface defects. It is found that in situ generation of a CoMoS active phase would take place to reach the best activity of our catalysts under the HDO reaction condition or by H2 prereduction treatment. With varying different Co–Mo molar ratios, the optimized CoMoS-0.18 catalyst exhibits the highest HDO activity, with a p-cresol conversion of 92.4% and a toluene selectivity of 95.5% at 250 °C. The high performance is ascribed to the formation of an accessible surface CoMoS phase after surface restructuring.

Stable and Selective Dehydrogenation of Methylcyclohexane using Supported Catalytically Active Liquid Metal Solutions – Ga52Pt/SiO2 SCALMS

AbstractThe use of gallium‐rich, Supported Catalytically Active Liquid Metal Solution (SCALMS) is a promising new concept to achieve catalysis with atomically dispersed active metal atoms. Expanding our previous work on short alkane dehydrogenation, we present here the application of SCALMS for the dehydrogenation of methylcyclohexane (MCH) to toluene (TOL) using a Ga52Pt alloy (liquid under reaction conditions) supported on silica. Cycloalkane dehydrogenation catalysis has attracted great attention recently in the context of hydrogen storage concepts using liquid organic hydrogen carrier (LOHC) systems. The system under investigation showed high activity and stable conversion of MCH at 450 °C and atmospheric pressure for more than 75 h time‐on‐stream (XMCH=15 %) with stable toluene selectivity (STOL) of 85 %. Compared to commercially available Pt/SiO2, the SCALMS system resulted in higher yields and robustness. Baseline experiments with Pt‐free Ga/SiO2 under identical conditions revealed the decisive influence of Pt dissolved in the liquid Ga matrix.

Engineering Adsorption Case for Efficient Capture of VOCs Using Biomass‐based Corncobs via a Carbonized Strategy

AbstractHerein, we report excellent corncobs‐derived carbon adsorbent by the special KOH chemical activation method which specific to selective adsorption removal of volatile organic chemicals (VOCs) under humid conditions. The obtained corncobs‐derived carbon adsorbent affords the enhanced adsorption removal capacities for volatile benzene (851.3 mg g‐1) and toluene (854.9 mg g‐1), outperforming comparative that derived from KOH grind means, which are 3 times higher than those of commercial activated‐carbon (benzene 275 mg g‐1, toluene 310.5 mg g‐1). We also demonstrated that the optimized structural property of the fabricated adsorbent had a good correlation with the adsorption efficiency of VOCs. Besides, the adsorption selectivity of benzene and toluene under different relative humidity distinguished by DIH (Difference of the Isosteric Heat) equation further indicates the beforehand adsorption behavior of toluene on the corncobs‐derived carbon adsorbent compared to benzene, which should be benefited from the improved synthetic tactics. Our study provides a real possibility for the practical engineering application of waste biomass (corncobs)‐derived engineering carbonaceous adsorbent in VOCs pollution control.

Catalytic co-pyrolysis of waste corn stover and high-density polyethylene for hydrocarbon production: The coupling effect of potassium and HZSM-5 zeolite

In this work, acid-washing corn stover (ACS) impregnated with various concentrations of potassium was co-pyrolyzed with high-density polyethylene (HDPE) in a fixed bed reactor. The coupling effect of potassium and HZSM-5 zeolite on product yields and mono-aromatic selectivity was studied. As the concentration of potassium increased, a reduction in liquid and an increase in gas and char yields were observed in both catalytic and non-catalytic co-pyrolysis. Potassium enhanced alkenes production with a maximum value of 54.2 % obtained from 0.8 wt%K-ACS/HDPE, indicating that potassium dispersed in char exerted catalytic effect on promoting the degradation of HDPE. Compared to ACS/HDPE, the catalytic co-pyrolysis of K-ACS/HDPE over HZSM-5 produced higher yield of mono-aromatics in the range of 77.3–82.5 % due to the fact that potassium optimized the co-pyrolysis intermediates diffused into HZSM-5 zeolite. The coupling effect of potassium and HZSM-5 also favored the selectivity of toluene and xylene while suppressed the selectivity of alkylnaphthalene. The ICP-MS result showed that only a trace amount of potassium was deposited on the HZSM-5 zeolite during the ex-situ catalytic co-pyrolysis process. The BET surface area and acidity of spent HZSM-5 zeolites increased and the coke amount decreased with the potassium concentration, indicating that potassium alleviated the deactivation of HZSM-5 zeolite by changing the yield and distribution of co-pyrolysis intermediates.