Acid Sites In Zeolites Research Articles

Metal cation exchange with zeolitic acid sites modulates hydrocarbon pool propagation during CO2 hydrogenation

Metal cation exchange with zeolitic acid sites modulates hydrocarbon pool propagation during CO2 hydrogenation

Novel Approach to Organization of Structured Cobalt-Based Fischer–Tropsch Catalyst

Structured Fischer–Tropsch synthesis catalysts were tested in tubular reactors of industry-standard diameters of 0.5 or 0.75 inches. The structured catalyst bed was manufactured by the obturation of a straight bunch of graphite-based extrudates (D = 1.5 mm, L = 30 mm). A conventional loose bed of granulated catalyst (D = 1.5 mm, L = 3 mm) was tested as a reference. In a 1000–3000 h−1 syngas space velocity range, structured and loose catalyst bed testing showed no significant differences in their main catalytic parameters. Nevertheless, their C5+ hydrocarbon group composition was quite different, i.e., the alkene fraction rose from 9 to 23%, while n-alkanes dropped from 81 to 64%. This could be a result of secondary reaction intensification in the conventional loose bed due to its zeolite acid site’s higher availability. Further FTS testing of the structured catalysts in 4000–6000 h−1 manifested distinctive limits in C5+ productivity for 0.5 and 0.75 inches of 512 kg C5+/(m3 reactor·h) and 362 kg C5+/(m3 reactor·h), respectively. This may be explained by limitations in structured bed thermal conductivity. It suggests that the arrangement of extrudates in the structured catalyst can significantly affect the reaction heat and mass transfer conditions and affords new opportunities for group composition control by means of catalyst bed organization.

Zeolite-modified alumina-bead catalyst for hierarchical cracking of bulky molecules

A novel zeolite-modified alumina-bead catalyst (ZSM-5/Al2O3-b) was prepared via calcining zeolite-coated alumina-bead material (Al2O3-b@ZSM-5) to graft zeolitic acid sites on the alumina-bead surface. The acid catalyst proved high activity and more 8 times catalytic efficiency than the corresponding ZSM-5(5 %) + Al2O3 mechanically mixed catalyst for cracking of 1, 3, 5-triisopropylbenzene (TIPB) in the FCC simulation reactor with short contact time. The characterization results showed that the surface property of the alumina-beads has been modified and the interface connection of Si-O-Al bonds between zeolitic nanoparticles and alumina resulted in stable zeolite particles on the alumina surface and the structural stability in hot water. The excellent catalytic performances are ascribed to the decrease of diffusion limitation of reactants and intermediates and the increase of Brønsted acid sites on the ZSM-5/Al2O3-b catalyst. The grafted/modified alumina-bead catalyst can be directly used in practical catalytic cracking of large molecules without forming. This strategy can be extended to the preparation of other types of zeolite-containing catalysts and industrial applications.

CO2‐Mediated Oxidative Dehydrogenation of Propane over Zn Modified SSZ‐39 Catalysts

AbstractTo reveal the catalytic function of Brønsted acid sites (BAS) and different Zn Lewis acid sites (LAS) over SSZ‐39 and Zn modified SSZ‐39 in the direct dehydrogenation of propane (DHP) and CO2‐mediated oxidative dehydrogenation (CO2‐ODHP) to propylene, a series of Zn‐modified H(Na)SSZ‐39 catalysts with various Zn loadings was prepared and conducted comparative studies between DHP and CO2‐ODHP. Detailed characterization results reveal the Zn‐loading‐dependent formation of Zn sites, primarily including Zn2+ and [Zn−O−Zn]2+, as well as their contributions in generating Lewis acid sites while neutralizing Brønsted acid sites of HSSZ‐39, namely bridged Si(OH)Al groups. In DHP, in comparison to bare HSSZ‐39, Zn/HSSZ‐39 catalysts exhibited a significantly enhanced C3H8 conversion. The presence of CO2 even further promoted C3H8 conversion in comparison to DHP. Given the above observations, we prepared Zn/NaSSZ‐39, in which the incorporation of Na further enriches the Lewis acid sites while neutralizing Brønsted acid sites of zeolite. Zn/NaSSZ‐39 even outperforms Zn/HSSZ‐39 catalysts with almost doubled C3H6 yield for CO2‐ODHP. The BAS has a poor CO2‐ODHP performance but can enhance the CO2 conversion towards CO significantly, while the Zn LAS is favorable for the CO2‐ODHP reaction, and plausible reaction paths of CO2‐ODHP on active sites are proposed.

Synergistic Effect of RuCo and Hierarchical ZSM‐5 for Enhanced Hydrogen Generation

AbstractA unique bifunctional catalyst comprised of acid site containing, hierarchical ZSM‐5 (contains acid sites) supported RuCo bimetal, was synthesized using a facile incipient wetness impregnation method. The synergistic interaction between zeolite acid sites and bimetals of this bifunctional material significantly improves its performance as a catalyst of hydrogen producing, dehydrogenation of ammonia borane.

Compound catalyst of ReMoSx@HSSZ-39 and SAPO-34 zeolites for high performance conversion of CO2 to C2-4 hydrocarbons

We report here a high-performance catalyst ReMoSx@HSSZ-39 compounded with SAPO-34 for conversion of CO2 to C2-4 hydrocarbons, in which the ReMoSx clusters are responsible for highly efficient hydrogenation of CO2 to methanol as the intermediate and then the surrounding zeolitic acid sites for further conversion of methanol to hydrocarbons. The investigation finds that uniform ReMoSx clusters can be reliably fabricated in zeolitic cages by co-introduction of rhenium and molybdenum species into the HSSZ-39 zeolite and followed by sulfidation, which constitutes an intimate bifunction catalyst through better cooperation of ReMoSx clusters and the zeolitic acid sites. Compared with MoSx@HSSZ-39, the introduction of rhenium significantly suppresses CO generation. By mixing some SAPO-34 zeolite, with increased density of protonic acid, more than 86 % C2-4 hydrocarbons in organic products and only 21 % CO at 32.5 % of CO2 conversion are obtained and the composite catalyst shows excellent stability with more than 95 % C2-4 hydrocarbons in organic products, less than 30 % CO and above 26.6 % of CO2 conversion after 1000 h on stream.

Assessing the Binding of Plastics Additives at Brønsted Acid Sites of Zeolites

Assessing the Binding of Plastics Additives at Brønsted Acid Sites of Zeolites

The dynamic catalysis of Ga/ZSM-5 catalysts for propane-CO2 coupling conversion to aromatics and syngas

Alkane coupling with CO2 by metal-containing zeolites catalysis is found to be a promising way to produce aromatics and syngas in recent years, but the real active sites and the role of CO2 are still unclear owing to the quick evolution of the metallic active sites and the complex reaction processes including direct propane aromatization, CO2 hydrogenation, reverse water–gas shift reaction, and propane-CO2 coupling aromatization. Herein, Ga/ZSM-5 catalysts were constructed to study the dynamic evolution of the metallic active sites and the role of CO2 during the propane and CO2 coupling reaction. After optimizing the reaction conditions, a notable propane conversion rate of 97.9% and an impressive aromatics selectivity of 80.6% in hydrocarbons can be achieved at the conditions of 550 °C and CO2/C3H8 of 4. 13CO2 isotope experiments illustrate that C-atoms of CO2 can enter into CO (86.5%) and aromatics (10.8%) during the propane-CO2 coupling reaction process. In situ XANES and FTIR spectroscopies at 550 °C and H2/C3H8 atmosphere reveal that GaOx species can be gradually dispersed into [GaH2]+/[GaH]2+ on the Brønsted acid sites of ZSM-5 zeolite during H2 and/or C3H8 treatment, which are the real active sites for propane-CO2 coupling conversion. In situ CO2-FTIR experiments demonstrate that the [GaH2]+/[GaH]2+ species can react with CO2 and accelerate the propane and CO2 coupling process. This work not only presents a cost-effective avenue for CO2 utilization, but also contributes to the active site design for improved alkane and CO2 activation in coupling reaction system.

Metal-acid synergistic catalysis accelerates the hydrogen borrowing amination of alcohols by confining Ru sites in Beta zeolite

Direct hydrogen transfer amination of alcohols with amines is an environmentally friendly and atom-economical route for the synthesis of N-alkylamines. Noble metal species are highly catalytic active sites, but the exorbitant price makes the urgency to boost the atom efficiency with stable recyclability. Herein, we demonstrated that encapsulation of Ru nanoparticles (NPs) within BEA zeolite through direct hydrothermal approach greatly promoted the catalytic efficiency in the N-alkylation of aromatic alcohols and amines under additive- and solvent-free conditions, resulting in the high yield (∼93 %), maximum turnover number (TON) of 12,822 and turnover frequency (TOF) of 9012 h−1, with stable recyclability and extendable substrate scope. The kinetic studies and in-situ characterizations revealed that the synergy of confined Ru NPs and adjacent acid sites of BEA zeolite significantly promoted the C–H bond activation in the rate-determining step of alcohol dehydrogenation into aldehydes. Besides, the acid sites also accelerated the condensation of aldehyde intermediates and anilines to promote the kinetic equilibrium, while the moderate strength of the Ru–H bond resulting from the confined Ru NPs is advantageous to balance the dehydrogenation and hydrogenation steps to reach the fascinating H-transfer process.

Conversion of Polypropylene into Light Hydrocarbons and Aromatics by Metal Exchanged Zeolite Catalysts.

Polyolefins can be converted into C2-C5 hydrocarbons and benzene-toluene-xylene (BTX) aromatics as high-demand petrochemical feedstocks via catalytic pyrolysis on acidic zeolites. Bro̷nsted and Lewis acid sites are responsible for cracking polyolefins into olefins and subsequent aromatic formation. In this study, we have subjected the parent HZSM-5 zeolite to postsynthetic partial metal exchange with Fe, Co, Ni, Cu, and Ce cations to perturb Bro̷nsted/Lewis acidity. We have investigated these metal-modified HZSM-5 on the catalytic pyrolysis of polypropylene (PP) in a micropyrolyzer connected to a two-dimensional gas chromatograph coupled to a time-of-flight mass spectrometer and flame ionization detector (Tandem Pyrolyzer-GC × GC-TOF-MS/FID setup). Whereas Fe-, Co-, Cu-, and Ce-exchanged zeolites (with 2.5, 2.3, 1.9, and 0.8 wt % metal, respectively) had comparable product yields with the parent zeolite, Ni-exchanged zeolites with Ni content of 0.5 to 2 wt % were associated with enhanced BTX formation (28-38 wt %) compared to that of the parent zeolite (22 wt %). Pyridine-FTIR indicated that the Bro̷nsted/Lewis acid ratio of the parent zeolite decreased upon metal ion exchange. According to Pyridine-TPD, the parent zeolite's medium-strength acid sites were redistributed into weak and strong acid sites in Ni-exchanged zeolites. The higher amount of carbon deposits on Ni-exchanged zeolites compared to the parent and other metal ion exchanged zeolites was attributed to the enhanced aromatization activity by the simultaneous decrease in the Bro̷nsted/Lewis acid ratio and emergence of strong acid sites.

Synthesis of tungsten iron-oxide zeolite composites and their catalytic degradation in VOC from rubber powder modified asphalt

Tungsten iron-oxide zeolite composites with different Fe and W loadings were synthesized over NaY zeolite supports using a wet impregnation method. The composites exhibited suitable textural properties, light absorption, redox sites and acidity for photocatalytic VOC degradation. The photocatalytic activity for degrading acetaldehyde and o-xylene VOCs emitted from rubber powder modified asphalt was evaluated under solar irradiation. The 5Fe-10 W-NaY(2.8) composite achieved the highest VOC removal of 80% for acetaldehyde and 76% for o-xylene after 6 hours. Increasing Fe and W loading up to 5 wt% and 10 wt%, respectively, significantly enhanced the VOC degradation efficiency. Higher zeolite content and stronger acidity also boosted the photocatalytic performance. The degradation occurred via redox mechanisms involving photo-generated electrons, holes and reactive oxygen species, facilitated by the zeolite acid sites. The 5Fe-10 W-NaY(2.8) composite exhibited good stability over 5 reuse cycles, indicating its potential for mitigating VOC emissions from rubber powder modified asphalt pavements.

Effective hierarchical ZSM‐5 catalysts for the cracking of naphtha and waste tire‐derived oil to light olefins

AbstractHierarchical ZSM‐5 zeolite materials with different SiO2/Al2O3 molar ratios in the range of 60–300 were synthesized using soft templating and microemulsion methods to generate zeolite materials with narrow mesopore size distributions. The resulting materials were characterized by X‐ray flourescence (XRF), Fourier transform infra‐red (FTIR) spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature programmed desorption (NH3‐TPD), thermo‐gravimetric analysis (TGA), Brunauer‐Emmett‐Teller (BET) surface area measurements, and products from the catalytic tests were analyzed by gas chromatography (GC). The XRF analysis determined that the Si/Al ratios for the synthesized ZSM‐5 were close to the batch ratios. The XRD and FTIR results revealed that the synthesized samples had crystalline ZSM‐5 zeolite structures. The small angle observed from the XRD patterns confirmed the presence of mesopores in the structure of the prepared materials. The SEM results showed that the ZSM‐5 synthesized materials had different morphologies and particle sizes, as well as worm‐like holes indicating that some macropores with average pore sizes ranging between 68 and 85 nm were successfully generated in these materials. NH3‐TPD results showed that the total acidity of the prepared materials decreased with an increase in the Si/Al (SA) ratio following this trend: SA = 71 > 177 > 345. This may be due to the decrease in the aluminum content, which is largely responsible for the formation of acidic sites in zeolites. The acid strength was found to increase with a decrease in the Si/Al ratio, highlighted by the peak shifts to higher temperatures. From the BET results, the SA = 71 was observed to have the highest SSA of 618 m2/g given by its micropore area of 103 m2/g and an external surface area of 515 m2/g. The high external surface area present in the material was due to the development of mesopores with narrow pore size distribution of approximately 6 nm indicating the success of the microemulsion method for the generation of hierarchical zeolites with well controlled pore sizes. The hierarchical ZSM‐5 catalysts were tested for the cracking of various hydrocarbon chain lengths. Low conversions, less than 10%, were obtained in the cracking of hexane; however, when cracking longer chain C12 hydrocarbons, the conversion increased remarkably to 100%. The catalyst with SA = 71 had the highest selectivity towards ethylene and propylene olefins due to its higher acidity in comparison with the other prepared catalysts. Improved activity, selectivity towards ethylene and propylene greater than 60%, and enhanced catalyst stability were demonstrated when using a hierarchical ZSM‐5 compared to the commercial catalyst in the cracking of dodecane. High selectivity towards light olefins was obtained for the cracking of waste tire‐derived oil. The results suggest that these hierarchical materials are suited to the cracking of long chain hydrocarbons and are promising materials for the valorization of waste tire‐derived oils.

Unravelling Irreversible Adsorbate Thermodynamics through Adsorption-Assisted Desorption.

Strongly bound surface species like alkylamines adsorbed on the Brønsted acid site of aluminosilicate zeolites exhibit negligible rates of molecular desorption, preventing them from achieving an equilibrated state on experimentally relevant time scales that limit the measurement of their adsorption thermodynamics. Through adsorption-assisted desorption, whereby distinct alkylamines facilitate desorption from Brønsted acid sites, we demonstrate that equilibrated states are achieved. Breakthrough adsorption measurements reveal that while 2-butylammonium on a Brønsted acid site is irreversibly adsorbed, it readily undergoes molecular desorption when exposed to a distinct alkylamine like 2-propanamine. As a result, two-adsorbate equilibrium was achieved when the Brønsted acid sites of aluminosilicate zeolites were exposed to a binary vapor-phase alkylamine mixture. By varying relative vapor-phase partial pressures and temperatures, we demonstrate the ability to experimentally measure the adsorption enthalpy and entropy of alkylammonium adsorbates on mostly isolated Brønsted acid sites in H-ZSM-5 (Si/Al = 140). A multiadsorbate Langmuir isotherm was found to quantitatively describe the coadsorption of alkylamines varying in size and basicity over a wide range of conditions through which the relative adsorption enthalpy and entropy of alkylamines were measured. Across a homologous family of sec-alkylamines (C3-C5) adsorbed on isolated Brønsted acid sites, a fixed contribution to the enthalpy (19 ± 4 kJ mol CH2-1) and entropy (25 ± 4 J mol CH2-1 K-1) of adsorption per methylene unit was found to exist, likely resulting from electrostatic interactions between the alkyl chain and the surrounding pore environment.

Highly selective conversion of COx to C2–4 hydrocarbons over MoSx@HSSZ-39 catalyst

Here, we report a high-performance catalyst MoSx@HSSZ-39 for conversion of COx to C2–4 hydrocarbons, in which MoSx clusters for COx hydrogenation at the first to intermediate methanol and then the zeolitic acid sites surrounding for further conversion of methanol to hydrocarbons. For CO2 hydrogenation, C2–4 hydrocarbons of ∼90% selectivity in organic products at 32.7% of CO2 conversion and excellent stability of 1000 h on stream are obtained. For CO hydrogenation, 95% of C2–4 hydrocarbons, 83% of LPG or 74% of propane selectivities at > 22% CO conversion and stable more than 200 h on stream are obtained. The cooperation among the MoSx clusters and the zeolitic acid sites constitutes the catalyst of intimate bifunction, which is the key to the high catalytic performance for COx hydrogenation.

Improvement of catalyst activity in cracking of n-hexane via metal (Fe/Ga) impregnation over ZSM-12 catalyst

In this research, zeolite ZSM-12 with Si/Al ratio = 80 was synthesized by hydrothermal method. The synthesized zeolite ZSM-12 was modified using Fe and Ga metals and a combination of these two metals, 1 % iron metals (Z80-Fe) and 1 % gallium metals(Z80-Ga), and a 2 % combination of these two metals (Z80-Fe-Ga). The physicochemical properties of synthesized zeolites were evaluated and compared by XRD, EDX-dot-mapping, NH3-TPD, BET, FT-IR, and TGA analyses. The catalytic assessment of synthesized zeolites in the HTO (n-hexane to olefins) process in a fixed bed reactor under atmospheric pressure and Weight hourly space velocity (WHSV) equal to 4 h−1 at 550 °C was evaluated. Various parameters such as selectivity towards light olefins, propylene to ethylene (P/E ratio), production of light alkanes, and aromatic compounds (BTX) were investigated. The results show that using metals led to the improvement and adjustment of the acid sites of zeolite, and the highest amount of light olefin and the lowest amount of coke were obtained. The result of the n-hexane to olefin process showed that the yield of light olefins was significantly improved in all modified catalysts compared to parent zeolite MTW. Compared to other modified zeolites, Z80-Fe-Ga zeolite has the highest yield of light olefins, equal to 59 %. This zeolite performs better due to the presence of gallium and iron metals and shows the highest propylene selectivity (P/E = 2.4). In addition, according to the results of the TGA analysis, the content of coke on the Z80-Fe-Ga catalyst after the catalytic reaction is much less than that of other catalysts after the catalytic reactor test.

Designing a Mordenite Catalyst with Enhanced Acidity for Dimethyl Ether Carbonylation by Engineering Open Sn Sites

Due to their tunable acidity, shape selectivity, and excellent stability, zeolites are of great importance as solid acid materials in industrial catalysis. Tuning the properties of the acid sites in zeolites allows for the rational design and fabrication of catalysts for target reactions. Dimethyl ether (DME) carbonylation, a critical chain-growth reaction for C1 resource utilization, is selectively catalyzed by the Brønsted acid sites within the eight-membered rings (8-MRs) of mordenite (MOR). It is anticipated that strengthening the Brønsted acidity—particularly in 8-MRs—will improve the catalytic performance of MOR. In this work, density functional theory (DFT) calculations are first employed and the results used to design a modified MOR with stannum (Sn) and to predict the corresponding changes in acidity. Guided by the theoretical studies, a series of Sn-modified MOR are synthesized via a defect-engineering and subsequent heteroatom-substitution strategy. After partial desilication, isolated tetrahedral Sn species in an open configuration are successfully synthesized for the first time, within which tetrahedrally coordinated Al sites are preserved. An acidic characterization is used to confirm that the acidity of the Brønsted acid sites is enhanced by the introduction of the Sn species; as a result, the sample exhibits excellent activity in DME carbonylation reaction. Kinetic and DFT studies reveal that this strengthened acidity facilitates the adsorption of DME and reduces the activation barriers of DME dissociation and acetyl formation, accounting for the improved activity. The work demonstrates mechanistic insights into the promoting effects of strong acidity on DME carbonylation and offers a promising strategy to precisely control the acidic strength of zeolites.

Effect of Zn–Brønsted acid in zeolites on ethane dehydrogenation with tandem reverse water gas shift reaction

The abundant hydroxyl groups and tunable Brønsted acid sites (BAS) of MWW zeolites were used to introduce and anchor zinc active sites, preventing the volatilization and deactivation of ZnOx due to its reduction to Zn0. Fabricated Zn/MWW catalysts effectively promoted ethane dehydrogenation (EDH) and tandem complex reaction of dehydroaromatization and CO2 oxidative dehydrogenation at high temperatures. Brønsted Zn/MWW catalysts containing [ZnOH]+ were prepared via incipient wetness impregnation using liquid ion exchange whereas those containing [ZnOx]2+ were prepared via atom planting using the gas dechlorination reaction. Additionally, the different acidic sites in MWW zeolites effectively affected the interaction between ZnCl2 and hydroxyl groups during the dechlorination reaction. The catalytic EDH performance of [ZnOx]2+ active sites generated using stronger BASs was higher than that of [ZnOx]2+ active sites generated via weaker BASs and silanol. The synergetic effect of Zn and BASs in zeolites catalyzed dehydroaromatization can be suppress by control the [ZnOH]+ location in the external surface of zeolite or by homogenous consumption of the BAS by [ZnOx]2+. Furthermore, [ZnOH]+ and [ZnOx]2+ catalyzed the reverse water gas shift reaction, accelerated the rate-limiting step of EDH via the CO2 oxidative EDH reaction, inhibited the selectivity of aromatics, and consumed coke via the Boudouard reaction.

Qualitative and quantitative analysis of Brønsted and Lewis acid sites in zeolites: A combined probe-assisted 1H MAS NMR and NH3-TPD investigation

Zeolite is one of the most important heterogeneous catalysts in acid catalytic reactions. Considering that the catalytic behaviors of zeolites are mostly related to their acidic characteristics, extensive attention has been attracted to the measurements of acid type, strength and concentration in zeolites. Numerous techniques including Fourier-transform infrared spectroscopy (FTIR), probe-assisted 1H, 13C and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) as well as temperature programmed desorption of ammonia (NH3-TPD) have been developed for determining the acid sites. Nevertheless, a single approach is defective to characterize the acid sites comprehensively. Herein, combining the probe-assisted (e.g., NH3 and CD3CN) 1H MAS NMR and NH3-TPD, the acid sites in different zeolites including the acid type, density and strength were determined. The commonly utilized NH3-TPD to determine the acid strength of zeolite samples with different topologies should be rigorously considered owing to zeolite confinement effect. Controlling the desorption temperature of NH3 probe molecules, the acid type (i.e., Brønsted acid sites (BAS) and Lewis acid sites (LAS)) and the corresponding density could be determined by NH3 probe-assisted 1H MAS NMR spectroscopy, while the acid strength could be investigated via CD3CN probe-assisted 1H MAS NMR spectroscopy.

Controlled reduction of spinel material for highly selective syngas aromatization over bifunctional catalysts

Directly converting syngas to aromatics allowed fossil fuel and biomass to provide high-value chemicals. Combining MnFe2O4 spinel material with ZSM-5 zeolite made obtaining a highly selective and stable bifunctional catalyst possible to overcome the present challenge in severe operating conditions and low aromatics content in liquid products. The precisely controlled catalyst exhibited an aromatics selectivity of 63.1 % at CO conversion of 38.3 %, leading to the content of aromatics in C5+ being higher than 95 %, ensuring that most liquid products are aromatic hydrocarbon (dominated by C6 ∼ C12 aromatics), which were significant for the separation and practical application in the syngas conversion process. Characterizations provided evidence of the partially reduced spinel material forming the tiny Fe5C2 particles as main active sites in CO conversion, and the formed olefins were further transformed into aromatics on acid sites of ZSM-5 zeolites. The results fully proved that the precise control of the content and proximity of each component was of great significance for the catalytic performance. Benefiting from the stable structure and potassium promoter, the reduction degree of the spinel material was controllably altered, achieving a significant improvement in aromatics selectivity. Moreover, the long-term stable reaction performance of the optimal catalyst indicated excellent application prospects for selectively converting syngas to aromatics. Thus, this work provided an idea to realize the aromatic production from syngas conversion by precisely controlling the exposure of the active centers.

Factors Affecting the Generation and Catalytic Activity of Extra-Framework Aluminum Lewis Acid Sites in Aluminum-Exchanged Zeolites

Factors Affecting the Generation and Catalytic Activity of Extra-Framework Aluminum Lewis Acid Sites in Aluminum-Exchanged Zeolites