scholarly journals Surface Characteristics Change of Zinc Modified H-ZSM-5 Zeolites in Methanol to Hydrocarbons Transformation Process

2020 ◽  
Vol 6 (11) ◽  
pp. 23-30
Author(s):  
A. Sidorov ◽  
V. Molchanov ◽  
L. Mushinskii ◽  
R. Brovko
Keyword(s):  
Surface Properties ◽  
Catalyst Deactivation ◽  
Catalyst Activity ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Transformation Process ◽  
Methanol To Hydrocarbons ◽  
Nitrogen Adsorption Isotherms

The t-plot method is a well-known method for determining the volumes of micro- and/or mesoporous materials and the specific surface area of a sample by comparison with a reference adsorption isotherm of a non-porous material having a similar surface chemical composition. The article describes the applicability of the t-graph method to the analysis of the surface properties of zinc modified samples of zeolite H-ZSM-5 before and after the reactions of methanol transformation into hydrocarbons occur on them. Zeolites are widely used as catalysts in the petrochemical and refining industries. These materials contain active Bronsted acid sites, distributed within the microporous structure of zeolites, which leads to selective catalysis due to the difference in the pore shape of the zeolites used. The size, shape of the zeolite catalyst determines the catalytic performance in terms of both product selectivity and catalyst deactivation. In most zeolite catalyzed hydrocarbon conversion reactions, catalyst activity is lost due to carbon deposition. In this connection, the determination of the surface properties of zeolites is an important task that contributes to the disclosure of the physicochemical essence of the process of deactivation of zeolites. The recalculation of nitrogen adsorption isotherms using the t-plot model made it possible to determine the volume of micro and mesopores. Based on the t-graph data, it can be concluded that during the transformation of methanol into hydrocarbons, carbon accumulates on the surface of the zeolite. In this case, the predominant deposition of carbon on the surface of mesopores, due to the fact that in the process of decontamination, from 61 to 73% of the volume of mesopores is lost. The number of micropores also decreases, but the share of losses is 42–54%, which is 10–15% lower compared to the loss of mesopore volume.

scholarly journals Influence of Topology and Brønsted Acid Site Presence on Methanol Diffusion in Zeolites Beta and MFI

Catalysts ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1342
Author(s):  
Cecil Botchway ◽  
Richard Tia ◽  
Evans Adei ◽  
Alexander O’Malley ◽  
Nelson Dzade ◽  
...  
Keyword(s):  
Molecular Diffusion ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Distribution Functions ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
A Value ◽  
Methanol To Hydrocarbons ◽  
Brönsted Acid ◽  
The Difference

Detailed insight into molecular diffusion in zeolite frameworks is crucial for the analysis of the factors governing their catalytic performance in methanol-to-hydrocarbons (MTH) reactions. In this work, we present a molecular dynamics study of the diffusion of methanol in all-silica and acidic zeolite MFI and Beta frameworks over the range of temperatures 373–473 K. Owing to the difference in pore dimensions, methanol diffusion is more hindered in H-MFI, with diffusion coefficients that do not exceed 10 × 10−10 m2s−1. In comparison, H-Beta shows diffusivities that are one to two orders of magnitude larger. Consequently, the activation energy of translational diffusion can reach 16 kJ·mol−1 in H-MFI, depending on the molecular loading, against a value for H-Beta that remains between 6 and 8 kJ·mol−1. The analysis of the radial distribution functions and the residence time at the Brønsted acid sites shows a greater probability for methylation of the framework in the MFI structure compared to zeolite Beta, with the latter displaying a higher prevalence for methanol clustering. These results contribute to the understanding of the differences in catalytic performance of zeolites with varying micropore dimensions in MTH reactions.

scholarly journals Mechanistic Insights into Hydrodeoxygenation of Acetone over Mo/HZSM-5 Bifunctional Catalyst for the Production of Hydrocarbons

Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 53
Author(s):  
Kai Miao ◽  
Tan Li ◽  
Jing Su ◽  
Cong Wang ◽  
Kaige Wang
Keyword(s):  
Hydrogen Pressure ◽  
Catalyst Deactivation ◽  
Catalyst Activity ◽  
Coke Formation ◽  
Bifunctional Catalyst ◽  
Acid Sites ◽  
Coke Deposition ◽  
Enhanced Production ◽  
Bio Oil ◽  
Catalytic Hydropyrolysis

Catalytic hydropyrolysis via the introduction of external hydrogen into catalytic pyrolysis process using hydrodeoxygenation catalysts is one of the major approaches of bio-oil upgrading. In this study, hydrodeoxygenation of acetone over Mo/HZSM-5 and HZSM-5 were investigated with focus on the influence of hydrogen pressure and catalyst deactivation. It is found that doped MoO3 could prolong the catalyst activity due to the suppression of coke formation. The influence of hydrogen pressure on catalytic HDO of acetone was further studied. Hydrogen pressure of 30 bar effectively prolonged catalyst activity while decreased the coke deposition over catalyst. The coke formation over the HZSM-5 and Mo/HZSM-5 under 30 bar hydrogen pressure decreased 66% and 83%, respectively, compared to that under atmospheric hydrogen pressure. Compared to the test with the HZSM-5, 35% higher yield of aliphatics and 60% lower coke were obtained from the Mo/HZSM-5 under 30 bar hydrogen pressure. Characterization of the spent Mo/HZSM-5 catalyst revealed the deactivation was mainly due to the carbon deposition blocking the micropores and Bronsted acid sites. Mo/HZSM-5 was proved to be potentially enhanced production of hydrocarbons.

scholarly journals Metal Chlorides Grafted on SAPO-5 (MClx/SAPO-5) as Reusable and Superior Catalysts for Acylation of 2-Methylfuran Under Non-Microwave Instant Heating Condition

Processes ◽  
2020 ◽  
Vol 8 (5) ◽  
pp. 603
Author(s):  
Ismail Alhassan Auwal ◽  
Ka-Lun Wong ◽  
Tau Chuan Ling ◽  
Boon Seng Ooi ◽  
Eng-Poh Ng
Keyword(s):  
Thermochemical Treatment ◽  
Nitrogen Adsorption ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Homogeneous Distribution ◽  
Covalent Bonds ◽  
Metal Chlorides ◽  
Promising Alternative ◽  
Highly Active ◽  
Catalyst Reusability

Highly active metal chlorides grafted on silicoaluminophosphate number 5, MClx/SAPO-5 (M = Cu, Co, Sn, Fe and Zn) catalysts via simple grafting of respective metal chlorides (MClx) onto SAPO-5 are reported. The study shows that thermochemical treatment after grafting is essential to ensure the formation of chemical bondings between MClx and SAPO-5. In addition, the microscopy, XRD and nitrogen adsorption analyses reveal the homogeneous distribution of MClx species on the SAPO-5 surface. Furthermore, the elemental microanalysis confirms the formation of Si–O–M covalent bonds in ZnClx/SAPO-5, SnClx/SAPO-5 and FeClx/SAPO-5 whereas only dative bondings are formed in CoClx/SAPO-5 and CuClx/SAPO-5. The acidity of MClx/SAPO-5 is also affected by the type of metal chloride grafted. Thus, their catalytic behavior is evaluated in the acid-catalyzed acylation of 2-methylfuran under novel non-microwave instant heating conditions (90–110 °C, 0–20 min). ZnClx/SAPO-5, which has the largest amount of acidity (mainly Lewis acid sites), exhibits the best catalytic performance (94.5% conversion, 100% selective to 2-acetyl-5-methylfuran) among the MClx/SAPO-5 solids. Furthermore, the MClx/SAPO-5 solids, particularly SnClx/SAPO-5, FeClx/SAPO-5 and ZnClx/SAPO-5, also show more superior catalytic performance than common homogeneous acid catalysts (H2SO4, HNO3, CH3COOH, FeCl3, ZnCl2) with higher reactant conversion and catalyst reusability, thus offering a promising alternative for the replacement of hazardous homogeneous catalysts in Friedel–Crafts reactions.

scholarly journals Surface Characteristics of the Pure and Li2O-doped MoO3/Al2O3 System

1998 ◽  
Vol 16 (2) ◽  
pp. 127-134 ◽  
Author(s):  
G.A. El-Shobaky ◽  
Kh.A. Khalil
Keyword(s):  
Activation Energy ◽  
Calcination Temperature ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Ammonium Molybdate ◽  
Lithium Oxide ◽  
Sintering Process ◽  
The Mean ◽  
Nitrogen Adsorption Isotherms

Two series of MoO3/Al2O3 solids, having the nominal compositions 0.2MoO3: Al2O3 and 0.5MoO3:A12O3, were prepared by impregnating finely powdered Al(OH)3 samples with calculated amounts of ammonium molybdate solutions. The solids thus obtained were dried at 120°C and then calcined in air at temperatures varying between 400°C and 1000°C. The doped samples were prepared by treating Al(OH)3 with LiNO3 solutions prior to impregnation with ammonium molybdate. The dopant concentrations employed were 1.5 and 6.0 mol% Li2O, respectively. The surface characteristics, viz. the specific surface area (SBET), the total pore volume (VP) and the mean pore radius (r) of the various pure and doped solids were measured from nitrogen adsorption isotherms conducted at -196°C. The SBET data measured for different adsorbents calcined at various temperatures enabled the apparent activation energy for sintering (ΔE3) to be determined for all the adsorbents investigated. The results obtained reveal that the SBET value of the pure and doped solids decreased on increasing the calcination temperature in the range 400–1000°C. The decrease was, however, more pronounced when the calcination temperature increased from 500°C to 700°C due to the formation of Al2(MoO4)3. Lithium oxide doping decreased the SBET value of the solid samples investigated and also decreased the activation energy for sintering to an extent proportional to the amount of dopant present. The sintering process for the pure and doped solids proceeds, mainly, via a particle adhesion mechanism.

scholarly journals Surface Characterization of Zn-modified H-ZSM-5 Zeolites

2020 ◽  
Vol 6 (6) ◽  
pp. 48-54
Author(s):  
M. Dziuba ◽  
L. Mushinskii ◽  
R. Brovko ◽  
V. Doluda
Keyword(s):  
Surface Properties ◽  
Adsorption Isotherms ◽  
Surface Characterization ◽  
Technical Problem ◽  
Nitrogen Adsorption ◽  
Correct Choice ◽  
Test Surface ◽  
Frequent Use ◽  
Nitrogen Adsorption Isotherms

The surface properties of microporous aluminosilicates are of primary importance in chemical technology and catalysis. The determination of the surface area, pore volume, and pore size and size distribution for microporous aluminosilicates is a complex scientific and technical problem related to both accurate measurements and the correct choice of a mathematical model that adequately describes the physicochemical processes occurring on the test surface. Currently, t-plot, as-plot, Dubinin-Radushkevich model, Dillimore model and Horvath-Kawazoe model are frequently used, each of which has certain advantages and certain disadvantages, to determine micropores in the material. It should be noted that t-plot model found the most frequent use. This is a consequence of the good correlation of volumes and pore areas obtained with its help with theoretically calculated values for various materials. In this point, the article provides a calculation of Zn-modified zeolite H-ZSM-5 surface properties using the t-plot model, for which nitrogen adsorption isotherms were originally obtained. The nitrogen adsorption isotherms of the initial zeolite H-ZSM-5 can be attributed to the first type of isotherms, and the modified samples to the fourth type of isotherms according to Brunauer’s classification. It was found that the initial zeolite is a typical microporous zeolite of H-ZSM-5 type, while the modified samples are micro- and mesoporous materials. Calculation of nitrogen adsorption isotherms using the t-plot model allows to determine the volume of micro and mesopores, which varied in the range of 0.11–0.14 cm3/g for micropores and 0.04–0.07 cm3/g for mesopores. Based on the obtained data, it can be concluded that when zeolite is modified with zinc at a zinc concentration less than 15 wt.%, micropores are not filled with zinc, while mesopores are predominantly filled and an additional surface of zinc oxide is formed on the external surface of the zeolite.

scholarly journals Natural and Chemically Modified Post-Mining Clays—Structural and Surface Properties and Preliminary Tests on Copper Sorption

Minerals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 704
Author(s):  
Beata Jabłońska ◽  
Mark Busch ◽  
Andriy V. Kityk ◽  
Patrick Huber
Keyword(s):  
Structural Properties ◽  
Surface Properties ◽  
Structural Changes ◽  
Low Cost ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Raw Material ◽  
Water Pretreatment ◽  
Maximum Sorption ◽  
Nitrogen Adsorption Isotherms

The structural and surface properties of natural and modified Pliocene clays from lignite mining are investigated in the paper. Chemical modifications are made using hydrofluoric acid (HF), sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid (HNO3), sodium hydroxide (NaOH), and hydrogen peroxide (H2O2), at a concentration of 1 mol/dm3. Scanning electron microscopy is used to detect the morphology of the samples. Nitrogen adsorption isotherms were recorded to determine the specific surface area (SSA), mesoporosity, microporosity, and fractal dimensions. The raw clay has an SSA of 66 m2/g. The most promising changes in the structural properties are caused by modifications with HF or H2SO4 (e.g., the SSA increased by about 60%). In addition, the raw and modified clays are used in preliminary tests with Cu(II) sorption, which were performed in batch static method at initial Cu(II) concentrations of 25, 50, 80, 100, 200, 300, and 500 mg/dm3 in 1% aqueous suspensions of the clayey material. The maximum sorption of Cu(II) on the raw material was 15 mg/g. The structural changes after the modifications roughly reflect the capabilities of the adsorbents for Cu(II) adsorption. The modifications with HF and H2SO4 bring a similar improvement in Cu(II) adsorption, which is around 20–25% greater than for the raw material. The structural properties of investigated clays and their adsorptive capabilities indicate they could be used as low-cost adsorbents (e.g., for industrial water pretreatment).

scholarly journals Precursor type affecting surface properties and catalytic activity of sulfated zirconia

2007 ◽  
pp. 105-113 ◽  
Author(s):  
Aleksandra Zarubica ◽  
Goran Boskovic
Keyword(s):  
Catalytic Activity ◽  
Beneficial Effect ◽  
Surface Properties ◽  
Sulfated Zirconia ◽  
Tetragonal Phase ◽  
Catalyst Activity ◽  
Sol Gel ◽  
Surface Characteristics ◽  
Zirconium Hydroxide ◽  
Catalytic Activities

Zirconium-hydroxide precursor samples are synthesized from Zr-hydroxide, Zr-nitrate, and Zr-alkoxide, by precipitation/impregnation, as well as by a modified sol-gel method. Precursor samples are further sulphated for the intended SO4 2- content of 4 wt.%, and calcined at 500-700oC. Differences in precursors? origin and calcination temperature induce the incorporation of SO4 2- groups into ZrO2 matrices by various mechanisms. As a result, different amounts of residual sulphates are coupled with other structural, as well as surface properties, resulting in various catalytic activities of sulphated zirconia samples. Catalyst activity and selectivity are a complex synergistic function of tetragonal phase fraction, sulphates contents, textural and surface characteristics. Superior activity of SZ of alkoxide origin can be explained by a beneficial effect of meso-pores owing to a better accommodation of coke deposits.

scholarly journals Surface Characteristics and Cracking Activity of MoO3–AlPO4 Catalysts

1998 ◽  
Vol 16 (1) ◽  
pp. 11-19 ◽  
Author(s):  
M.R. Mostafa
Keyword(s):  
Surface Acidity ◽  
Textural Properties ◽  
Nitrogen Adsorption ◽  
Surface Characteristics ◽  
Acid Sites ◽  
Acidic Properties ◽  
Texture Surface ◽  
First Order ◽  
First Order Kinetics ◽  
Cracking Reaction

Pure AlPO4 and MoO3–AlPO4 impregnated catalysts of different compositions have been prepared. The catalysts were characterized using XRD and IR techniques. The textural properties were determined from nitrogen adsorption at 77 K. The acidic properties of these catalysts were measured by the amine titration method. The cracking of cumene at flow rates of 20–60 ml/min and at 653–713 K was investigated over these catalysts. Loading AlPO4 with MoO3 leads to a significant change in texture, surface acidity and catalytic activity of the prepared catalysts. The cracking reaction over the investigated catalysts followed first-order kinetics with activation energies of between 8.0 and 20 kcal/mol. The cracking activity has been related to Brönsted acid sites present on the catalyst surface.

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