Benzene Selectivity Research Articles

Pt/Ni wet impregnated over Al incorporated mesoporous silicates: a highly efficient catalyst for anisole hydrodeoxygenation

This work reports, formation of benzene from anisole via hydrodeoxygenation process using vapour phase fixed bed reactor. The surface properties of bimetallic catalysts such as textural properties, acidic, and Pt/Ni dispersion has established by various characterization techniques. The reaction was carried out at 370 and 420 °C with space velocity 3.3 & 6.6 h− 1, over acidic and non-acidic supported mono and bimetallic catalysts. The optimum conversion and selectivity was observed at 420 °C and WHSV = 3.3 h− 1 for all mono and bimetallic catalysts. Pt/Ni/Al-SBA-15 acidic bimetallic catalyst shows maximum anisole conversion 59% with benzene selectivity 37% under atmospheric pressure, due to the more acidic centres and high dispersion of Pt/Ni species on the bimetallic catalyst, enhance the anisole conversion; this was proved by NH3-TPD and HR-TEM analysis. The acidic Pt/Ni bimetallic catalyst shows higher anisole conversion as compared to the mono metallic Pt/Ni catalysts and it works predominantly through demethylation and hydrogenolysis reaction pathway.

Catalytic Activity of Fe-SBA-15 Prepared by Evaporation-Induced Self-Assembly (EISA) Method

Fe-SBA-15 materials with different Fe content have been prepared using tetraethyl orthosilicate (TEOS) and iron nitrate (Fe (NO3)3·H2O as precursors and Pluronic P123 as structure directing agent through evaporation-induced self-assembly (EISA) method. The materials were characterized by nitrogen sorption, powder X-ray diffraction and TEM. All the Fe-SBA-15 samples appeared ordered 2D hexagonal mesostructure. The BET surface area and pore diameter were about 500 m2/g and 4 nm respectively. In the reaction of phenol hydroxylation to dihydroxybenzenes, the Fe-SBA-15 materials showed good catalytic activity, giving 20.2% of phenol conversion, 58.2% of selectivity for o-dihydroxy benzene and 41.8% of selectivity for p-dihydroxy benzene. After five cycles, the product yield was 25.2%, while selectivities of o-dihydroxy benzene and p-dihydroxy benzene were 58.2% and 41.8%, respectively. All these findings indicated the potential of Fe-SBA-15-10 could be used as a cost-effective, environment-friendly catalyst.

The Influence of Water on the Performance of Molybdenum Carbide Catalysts in Hydrodeoxygenation Reactions: A Combined Theoretical and Experimental Study

AbstractUnderstanding the deactivation of transition‐metal carbide catalysts during hydrodeoxygenation (HDO) reactions is of great importance for improving the production of the second generation fuels from biomass. Based on a combined experimental and theoretical study, we present a mechanistic model for the deactivation of molybdenum carbide catalysts during phenol HDO in the presence of water. At increased water pressure, water molecules preferentially bind to the surface, and active sites are no longer accessible for phenol. In line with first principle calculations, experiments reveal that this process is fully reversible because the reduction of the water partial pressure results in a threefold increase in conversion. The direct deoxygenation of phenol was calculated to be the most favorable pathway, which is governed by the structure of the phenol adsorption complex on the surface at high hydrogen coverage. This is consistent with the experimentally observed high benzene selectivity (85 %) for phenol HDO over MoCx/HCS (hollow carbon spheres) catalyst.

Model-Based Design of Experiments for Kinetic Study of Anisole Upgrading Process over Pt/γAl2O3: Model Development and Optimization by Application of Response Surface Methodology and Artificial Neural Network

Abstract The kinetic of catalytic upgrading of anisole as a lignin−derived bio−oil component is investigated experimentally over Pt/γAl2O3 at 573−673 K and 14 bar. According to experimental results, benzene, phenol, 2−methylphenol, 2,6−dimethylphenol, 2,4,6−trimethylphenol, and hexamethylbenzene are identified as the main products. The results indicated that the kinetically significant reaction classes are hydrogenolysis, hydrodeoxygenation (HDO), alkylation, and hydrogenation. The response surface methodology (RSM) is applied to optimize the experimental data which obtained at suggested conditions by design of experiment (DOE). Due to the complex nature of the system, artificial neural networks (ANNs) were employed as an efficient tool to model the behavior of the system. RSM and ANN methods were constructed based upon the DOE’s points and then utilized for generating extra−simulated data. Data simulated by the RSM/ANN method were used to fit power law kinetic rate expressions for the reactions. The coefficient of determination (R2 ) was obtained 0.998 and 0.973 for anisole conversion model and benzene selectivity model which represented the high accuracy of model predictions. The correlation coefficient (R) and mean square error (MSE) of ANN model equaled to 0.97 and 8.3 × 10−12 respectively means high accuracy of the developed model. The results of kinetic modeling with simulated data from the ANN and RSM models revealed that the highest reaction order during the upgrading process of anisole belongs to hydrogenolysis of anisole to phenol. Also the activation energy of hydrogenolysis reaction was lower than HDO.

Plasma-Assisted Non-Oxidative Conversion of Methane over Mo/HZSM-5 Catalyst in DBD Reactor

Methane utilization has been recognized as a challenging research topic because methane is very stable with strong C–H bond. Many efforts have been devoted to find an effective method for the methane activation. In this work, we examined the feasibility of decreasing the temperature of a non-oxidative methane dehydroaromatization by using DBD plasma-catalyst hybrid system. Mo/HZSM-5 catalyst was prepared and then it was used for the DBD plasma-assisted methane dehydroaromatization reaction. When the DBD plasma was applied to the Mo/HZSM-5 catalytic reactor, methane was converted at much lower temperatures than the conventional methane dehydroaromatization process. It was also confirmed that benzene selectivity could be improved by enhancing the interaction between plasma and catalyst. These results imply that the non-oxidative methane dehydroaromatization could occur effectively at milder conditions than the conventional process by using the optimized DBD plasma-catalyst hybrid system. Moreover, it was observed that the catalyst deactivation was effectively prevented when H2 gas was mixed with the reaction feed.

Metal salts with highly electronegative cations as efficient catalysts for the liquid-phase nitration of benzene by NO2 to nitrobenzene

Metal salts with highly electronegative cations have been used to effectively catalyze the liquid-phase nitration of benzene by NO2 to nitrobenzene under solvent-free conditions. Several salts including FeCl3, ZrCl4, AlCl3, CuCl2, NiCl2, ZnCl2, MnCl2, Fe(NO3)3∙9H2O, Bi (NO3)3∙5H2O, Zr(NO3)4∙5H2O, Cu(NO3)2∙6H2O, Ni (NO3)2∙6H2O, Zn(NO3)2∙6H2O, Fe2(SO4)3, and CuSO4 were examined and anhydrous FeCl3 exhibited the best catalytic performance under the optimal reaction conditions. The benzene conversion and selectivity to nitrobenzene were both over 99%. In addition, it was determined that the metal counterion and the presence of water hydrates in the salt affects the catalytic activity. This method is simple and efficient and may have potential industrial application prospects.

The Influence of Hydrogen-Permeable Membranes and Pressure on Methane Dehydroaromatization in Packed-Bed Catalytic Reactors

Computational simulations are developed and applied to study the coupling of packed-bed methane dehydroaromatization (MDA) reactors with hydrogen-selective membranes, for the production of value-added fuels, particularly benzene. Detailed chemical kinetics for reforming over bifunctional Mo/H-ZSM-5 catalysts are validated against published literature, and simulations explore the effect of hydrogen removal and operating conditions. Although results reveal that membrane integration significantly increases conversion, the desired benzene selectivity decreases, due to the increased yield of undesired byproducts such as naphthalene. The benzene-to-naphthalene ratio depends strongly on hydrogen removal, and simulations demonstrate that hydrogen membranes are most beneficial at relatively high GHSV and relatively low catalyst temperature. Increasing pressure decreases conversion and benzene selectivity, but increases benzene production rates and does not affect naphthalene selectivity. Single-pass benzene yield ...

Catalytic Upgrading of Fast Pyrolysis Products with Fe-, Zr-, and Co-Modified Zeolites Based on Pyrolyzer–GC/MS Analysis

To explore the influence of Fe-, Zr-, and Co-modified zeolites on bio-oil characteristics, the catalytic fast pyrolysis of cellulose combined with sawdust and cotton stalk was investigated using a pyrolyzer reactor. The results indicate that Fe-loaded zeolite favors naphthalene and 1-methylnaphthalene formation through catalytic deoxygenation and hydrocarbon formation. Zr-modified zeolite enhances the contents of ketones and aromatics with higher benzene and p-xylene selectivity. Co leads to higher production of anhydrous sugars but suppresses the progress of aromatics evolution, whereas the selectivity of Co for toluene and p-xylene is the highest. A comprehensive reaction network is also proposed to describe the cellulose catalytic pyrolysis process. Considering the catalytic adaptability, catalytic pyrolysis of typical biomass samples with Fe/HZSM-5 was investigated. The total contents of aromatic hydrocarbons are in the following order: sawdust > cellulose > cotton stalk. The selectivities of naphthal...

Epitaxial Growth of Oriented Metalloporphyrin Network Thin Film for Improved Selectivity of Volatile Organic Compounds.

This study reports an oriented and homogenous cobalt-metalloporphyrin network (PIZA-1) thin film prepared by liquid phase epitaxial (LPE) method. The thickness of the obtained thin films can be well controlled, and their photocurrent properties can also be tuned by LPE cycles or the introduction of conductive guest molecules (tetracyanoquinodimethane and C60 ) into the PIZA-1 pores. The study of quartz crystal microbalance adsorption confirms that the PIZA-1 thin film with [110]-orientation presents much higher selectivity of benzene over toluene and p-xylene than that of the PIZA-1 powder with mixed orientations. These results reveal that the selective adsorption of volatile organic compounds highly depends on the growth orientations of porphyrin-based metal-organic framework thin films. Furthermore, the work will provide a new perspective for developing important semiconductive sensing materials with improved selectivity of guest compounds.

Ni‐W Catalysts Supported on HZSM‐5/HMS for the Hydrogenation Reaction of Aromatic Compounds: Effect of Ni/W Ratio on Activity, Stability, and Kinetics

ABSTRACTNi‐W/HZSM5‐HMS catalysts were evaluated for the benzene hydrogenation reaction at 130–190°C. To study the catalyst characterization, X‐ray diffraction, X‐ray fluorescence, Fourier transform infrared, UV–vis, diffuse reflectance spectra, temperature‐programmed desorption of NH3, FT‐IR of adsorbed pyridine measurements (Py‐IR), H2 chemisorption, nitrogen adsorption–desorption, and TGA techniques were used. Kinetics of benzene hydrogenation was investigated under various hydrogen and benzene pressures, and the effect of reaction conditions on catalytic performance was studied. The results showed that bimetallic catalysts have better ability than a monometallic catalyst (Ni/HZSM5‐HMS) for this reaction, such as maximum benzene conversion (100%), minimum toluene conversion (1.76–40%), very low converted xylene, benzene selectivity (100%), good catalytic stability against coke deposition, and appropriate kinetic parameters.

Novel Immobilized Ionic Liquid Catalysts based on Micro/Mesoporous Materials

Several kinds of novel porous materials, including micro/mesoporous composites were successfully synthesized by the double template method, which combined P123 and ionic liquids. The obtained porous materials were investigated by XRD and nitrogen adsorption–desorption. The results proved the basic structure of micro/mesoporous materials. Three kinds of Lewis acid ionic liquid catalysts were immobilized onto these porous materials by impregnation, and their catalytic performances were investigated in Friedel–Crafts alkylation between benzene and 1-dodecene. Results showed that clearer micro/mesoporous materials benefit to increase of 2-LAB (2-position-substituted linear alkyl benzene) selectivity.

Benzene alkylation with methanol over phosphate modified hierarchical porous ZSM-5 with tailored acidity

Abstract The acidity and acid distribution of hierarchical porous ZSM-5 were tailored via phosphate modification. The catalytic results showed that both benzene conversion and selectivity of toluene and xylene increased with the presence of appropriate amount of phosphorus. Meanwhile, side reactions such as methanol to olefins related with the formation of by-product ethylbenzene formation and isomerization of xylene to meta -xylene were suppressed efficiently. The acid strength and sites amount of Bronsted acid of the catalyst were crucial for improving benzene conversion and yield of xylene, whereas passivation of external surface acid sites played an important role in breaking thermodynamic equilibrium distribution of xylene isomers.

Microwave-assisted catalytic fast pyrolysis of spent edible mushroom substrate for bio-oil production using surface modified zeolite catalyst

In order to minimize coke yield and improve hydrocarbon production during microwave-assisted catalytic fast pyrolysis of spent edible mushroom substrate, ZSM-5 zeolite catalyst is modified with pre-coking treatment, chemical vapor deposition of SiO2, and ethylene diamine tetraacetie acid (EDTA) chemical modification method, respectively (labeled PC-ZSM-5, SiO2-ZSM-5 and EDTA-ZSM-5). Experimental results show that all the modification methods result in a loss of external acid sites of ZSM-5. Among the three modified catalysts, the maximum oil fraction yield and the minimum coke yield are obtained with SiO2-ZSM-5. The relative content of hydrocarbons in oil fraction increases in the following order: SiO2-ZSM-5>EDTA-ZSM-5>PC-ZSM-5>original ZSM-5. Moreover, SiO2-ZSM-5 shows the highest relative contents of toluene and xylene, whereas original ZSM-5 produces the lowest ones. Besides, the selectivity of benzene in aromatics follows the order of original ZSM-5>EDTA-ZSM-5>PC-ZSM-5>SiO2-ZSM-5, while the selectivity of toluene+xylene presents the opposite trend.

Coke accumulation and deactivation behavior of microzeolite-based Mo/HZSM-5 in the non-oxidative methane aromatization under cyclic CH4-H2 feed switch mode

The lifetime deactivation patterns of a microzeolite-based 6wt%Mo/HZSM-5 in the non-oxidative dehydroaromatization of methane were measured first at 1073K and a space velocity of 12,000ml/g-Cat/h in continuous CH4-feeding, cyclic 5min CH4–5min He feed switch and cyclic 5min CH4–5min H2 feed switch modes. Appearance of an obvious inflection point in the course of benzene selectivity under the cyclic CH4-H2 feed switch operation mode revealed the two stages deactivation feature of the catalyst: the deactivation was first slow and then accelerated. TG and TPO measurements of the spent samples were performed and the results exhibited strong similarity in the total coke content and the intensity and area of the low temperature TPO-COx peak. Then, a set of tests under the cyclic CH4-H2 feed switch mode over different time frames, followed by the TPO measurements of the spent samples, was performed to pursue the coke accumulation behavior of the catalyst over its lifetime. The low-temperature burning coke defined by the low-temperature TPO-COx peak was confirmed to be the dominant type of coke, reside on the external surface of the zeolite and in the inner mouth region of the zeolite channels, and accumulate over the catalyst lifetime at a constant rate. In parallel, a constant rate was also observed for the decrease of the benzene formation rate itself over the slow deactivation period. While these observations suggest the possible existence of a cause and effect relationship between the low-temperature burning coke and catalyst deactivation, a detailed discussion was made on the dominant effect of accumulation of graphite-like coke on the slow deactivation of catalyst.

Development of metal organic framework-199 immobilized zeolite foam for adsorption of common indoor VOCs

Reticulated foam shaped adsorbents are more efficient for the removal of volatile organic compounds (VOCs), particularly from low VOC-concentration indoor air streams. In this study composite structure of zeolite and metal organic frameworks (MOFs), referred as ZMF, has been fabricated by immobilization of fine MOF-199 powder on foam shaped Zeolite Socony Mobil-5 (ZSM-5) Zeolitic structure, referred as ZF. The ZMF possess a uniform and well-dispersed coating of MOF-199 on the porous framework of ZF. It shows higher surface area, pore volume, and VOCs adsorption capacity, as compared to ZF-structure. Post-fabrication changes in selective adsorption properties of ZMF were studied with three common indoor VOCs (benzene, n-hexane, and cyclohexane), using gravimetric adsorption technique. The adsorption capacity of ZMF with different VOCs follow the order of benzene>n-hexane>cyclohexane. In comparison with MOF-199 and ZF, the composite structure ZMF shows improvement in selectivity for benzene from other two VOCs. Further, improvement in efficiency and stability of prepared ZMF was found to be associated with its high MOF loading capacity and unique morphological and structural properties. The developed composite structure with improved VOCs removal and recyclability could be a promising material for small to limited scale air pollution treatment units.

Cyclohexane dehydrogenation over Ni-Cu/SiO2 catalyst: Effect of copper addition

A series of Ni-Cu/SiO2 catalysts were prepared by sol-gel method for use in the dehydrogenation of cyclohexane to evolve hydrogen. The Ni/SiO2 catalyst exhibits excellent catalytic activity but low selectivity, due to the highly dispersion of Ni species. After the addition of Cu, the Ni-Cu nanoparticles with narrow size distribution (3–6nm) and a uniform structure of bimetallic Ni and Cu has been formed, and it drastically improves the selectivity to benzene. A 94.9% conversion of cyclohexane with 99.5% benzene selectivity was observed at 350°C in a continuous fixed bed flow reactor.

Effect of weak base modification on ZSM‐5 catalyst for methanol to aromatics

The effect of weak base modification on the catalytic performance of ZSM‐5 catalyst for conversion of methanol to aromatics was investigated. The catalysts were characterized using X‐ray diffraction, X‐ray fluorescence, N2 adsorption–desorption, NH3 temperature‐programmed desorption, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetry. The results showed that catalysts treated with weak base (NaHCO3, Na2CO3 and NH3⋅H2O) exhibited a pore structure with interconnected micropores and mesopores. The existence of mesopores was beneficial for improving the diffusion of reactants and products, and the coke deposition resistance capacity of treated catalysts was enhanced greatly. Meanwhile, compared to traditional ZSM‐5 zeolite, the ratio of Brønsted to Lewis (B/L) acid sites of ZSM‐5/NH3⋅H2O (B/L = 7.35) zeolite slightly increased but the amount of acid sites reduced, while those of ZSM‐5/NaHCO3 (B/L = 0.127) and ZSM‐5/Na2CO3 (B/L = 0.107) significantly reduced. Further, the catalyst treated with NH3⋅H2O solution was evaluated in the methanol to aromatics reaction and led to an enhanced aromatization reaction rate. The liquid hydrocarbons product distribution exhibited higher aromatic hydrocarbons yield (56.12%) and selectivity (40.28%) of benzene, toluene and xylene (BTX) with isoparaffin content reducing to 26.17%, which could be explained by appropriate B/L acid sites ratio, higher pore volumes and higher surface area.

Reduction of Catalyst Deactivation Effects on Styrene Monomer Production in Multistage Radial Fixed Bed Reactor

In the present study, ethylbenzene dehydrogenation to styrene monomer over a potassium-promoted iron oxide catalyst in radial fixed bed reactor was simulated. The pseudo-heterogeneous model was employed to predict ethylbenzene conversion and selectivity of styrene monomer, toluene, and benzene. The simulation results showed that deactivation of catalysts causes reduction in the reaction zone; therefore, the ethylbenzene conversion decreases. It is proposed that, for compensating the conversion reduction, the feed temperature is increased 1 °C per 5 cm of deactivated length. Simulation results are in good agreement with the experimental data obtained from real plant.

Catalytic conversion of propane to BTX over Ga, Zn, Mo, and Re impregnated ZSM-5 catalysts

A systematic study of the comparative performances of 1wt.% and 3wt.% Ga, 1wt.% and 3wt.% Zn, 3wt.% Mo, and 3wt.% Re impregnated ZSM-5 catalysts for propane aromatization is presented. It was found that methane, ethene, ethane, benzene, toluene, and xylene are the major products on all of these catalysts at typical propane aromatization temperature (∼550°C). 3% Zn/ZSM-5 catalyst shows the highest propane conversion among all the tested catalysts with approximately 56% total selectivity toward benzene, toluene, and xylene (i.e., BTX) but lower selectivity to methane, ethene, and ethane (i.e., light hydrocarbons). In sharp contrast, 3% Mo/ZSM-5 catalyst shows the lowest activity with lower BTX selectivity but as high as 52% total selectivity toward methane, ethene, and ethane. Further, calculations indicate that 1% Zn/ZSM-5 catalyst displays the highest H2 and BTX formation rates (mmol/s/mol–metal), followed by 1% Ga, 3% Re, 3% Zn, and 3% Ga impregnated ZSM-5 catalysts, while 3% Mo/ZSM-5 catalyst shows remarkably lower H2 and BTX formation rates. This suggests that the addition of 1% Zn into ZSM-5 via impregnation significantly improves the dehydrogenation and subsequent chain growth reaction as well as cyclization, thereby favoring propane aromatization. However, compared to other promoters (i.e., Zn, Ga, and Re), the promotional effect of Mo over ZSM-5 is insignificant for propane aromatization, thus resulting in substantial formation of methane, ethene, and ethane.

Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5

We present a new class of catalysts, InMo-ZSM-5, which can be prepared by indium impregnation of Mo-ZSM-5. The incorporation of indium dramatically decreases coke formation during methane dehydroaromatization. The benzene and C2 hydrocarbons selectivity among total hydrocarbons over InMo-ZSM-5 remains comparable to that of Mo-ZSM-5 despite reduced methane conversion due to decreased coke formation. We found 1 wt% indium to be optimal loading for reducing coke selectivity to half that of Mo-ZSM-5. Characterization methods were not helpful in discerning the interaction of In with Mo but experiments with bimetallic 1In2Mo-ZSM-5 and mechanical mixture 1In+2Mo-ZSM-5 suggest that In and Mo need to be in close proximity to suppress coke formation. This is supported by temperature programmed reduction experiments which show that In incorporation leads to lower Mo reduction temperature in In2Mo-ZMS-5.