Acidic Zeolites Research Articles

Water structures on acidic zeolites and their roles in catalysis.

The local reaction environment of catalytic active sites can be manipulated to modify the kinetics and thermodynamic properties of heterogeneous catalysis. Because of the unique physical-chemical nature of water, heterogeneously catalyzed reactions involving specific interactions between water molecules and active sites on catalysts exhibit distinct outcomes that are different from those performed in the absence of water. Zeolitic materials are being applied with the presence of water for heterogeneous catalytic reactions in the chemical industry and our transition to sustainable energy. Mechanistic investigation and in-depth understanding about the behaviors and the roles of water are essentially required for zeolite chemistry and catalysis. In this review, we focus on the discussions of the nature and structures of water adsorbed/stabilized on Brønsted and Lewis acidic zeolites based on experimental observations as well as theoretical calculation results. The unveiled functions of water structures in determining the catalytic efficacy of zeolite-catalyzed reactions have been overviewed and the strategies frequently developed for enhancing the stabilization of zeolite catalysts are highlighted. Recent advancement will contribute to the development of innovative catalytic reactions and the rationalization of catalytic performances in terms of activity, selectivity and stability with the presence of water vapor or in condensed aqueous phase.

Highly efficient production of aromatics from C2H5Cl coupling with CO over H-zeolites

Zhu's team reported a route via coupling conversion of CO and C2H5Cl (an essential C2H2 derivative) catalyzed by acidic zeolites, which obtains 72% aromatics selectivity. This work provides a new insight for natural gas conversion on H-zeolites.

Alteration of acidity and porosity of Beta zeolite using fibrous silica for light olefin production

Traditional olefin production heavily depends on fossil fuels, which are a significant contributor to environmental issues. Methanol to olefin (MTO) is among non-fossil fuel alternatives to produce olefinic products from abundant resources, such as biomass, coal, and natural gas. Nevertheless, the catalytic reaction of MTO over commercial zeolite catalysts is hindered by their low activity, mainly due to the micropore structure and excessive acidity within the zeolite. Herein, Beta zeolite with fibrous silica structure was successfully synthesized via the microemulsion and Beta seed-assisted method. The catalysts were characterized using FESEM, N2 physisorption, and ammonia-TPD. FESEM results revealed a well-ordered spherical morphology of HFBETA with uniform particle size distribution. In surface analysis, the HFBETA exhibits higher BET surface area and mesopore volume compared to commercial HBETA by 35% and 86%, respectively. The introduction of fibrous silica within the Beta structure led to a significant drop in the acidity of the catalyst, as shown in ammonia-TPD results. These led to superior catalytic performance of HFBETA in the MTO process.

Exploring the effect of Brønsted acidity of MFI-type zeolites on catalytic cracking temperature of low density polyethylene

We verified the effects of the zeolite Brønsted acidity (acid strength, acid amount, location of acid sites, etc.) on the catalytic cracking temperature of low density polyethylene.

Brønsted acid sites in the Beta zeolite induced highly efficient amidation of styrene in the aqueous phase

The acidic mesoporous Beta zeolite, which contains a substantial number of Brønsted acid sites, has been found to efficiently catalyze the amidation of styrene with benzonitrile in the aqueous phase.

Effects of zeolite porosity and acidity on catalytic conversion of carbohydrates to bio-based chemicals: a review

Optimizing the production process of high value-added chemicals derived from renewable biomass holds immense promise for clean energy utilization and environmental sustainability.

Selective linear ethylene oligomerization over nickel-containing zeotypes with tetravalent framework heteroatoms

Nickel-containing Lewis acidic zeolites as highly selective ethylene oligomerization catalysts.

Influence of aluminum zoning toward external surfaces in MFI zeolites on propene oligomerization catalysis.

Brønsted acid zeolites catalyze alkene oligomerization reactions, an important route to produce fuels and chemicals from light hydrocarbon feedstocks. Propene dimerization rates (per H+, 503 K) decrease monotonically with increasing crystallite size in MFI zeolites because heavy oligomer products remain occluded within microporous voids and restrict intrazeolite diffusion of reactants and products. Here, we show that the preferential zoning of framework Al centers and their associated H+ sites toward exterior surfaces of MFI crystallites in an "egg-shell" architecture minimizes the extent of diffusion-enhanced secondary reactions within a given crystallite, which increases both propene dimerization rates (per H+) and selectivity to true oligomer products. These results show that tailoring Al distributions to be spatially zoned toward external surfaces of medium-pore zeolite crystallites is efficacious at minimizing diffusion path lengths to increase alkene oligomerization rates and selectivity to true oligomer products.

In-situ catalytic pyrolysis of cellulose with lithium-ion battery ternary cathodes and ex-situ upgrading over Ru/HZSM-5 for bio-aromatics

Bio-aromatics preparation via in-situ catalytic pyrolysis of cellulose with lithium-ion battery ternary cathodes and ex-situ upgrading over Ru/HZSM-5 was studied. Three ternary cathodes with different ratios of Ni, Co, and Mn (NCM111, NCM532 and NCM811) were selected, and the effects of ternary cathodes and bifunctional Ru/HZSM-5 on the cellulose conversion were investigated from the perspectives of thermogravimetric kinetics and fixed-bed upgrading. The results indicated that cellulose pyrolyzed with cathodes reduced the solid residue content from 13.07% to 7.78%, 7.11%, and 6.63%, and decreased the weightlessness peak temperature from 358 ℃ to 348 ℃, 347 ℃, and 341 ℃; herein, the reaction order gradually elevated from 1.34 to 1.67 with the increased cathode Ni ratio, but the activation energy and pre-exponential factor obviously reduced. In-situ catalytic pyrolysis of ternary cathodes combined with ex-situ upgrading of Ru/HZSM-5 resulted in more cellulose-derived products being converted, increasing bio-oil yield from 22.47% to 25.08%, 24.75%, and 25.42%. Furfural was largely deoxygenated and dehydrated to become the precursor of aromatics, so NCM111, NCM532 and NCM811 usage increased the MAHs selectivity from 28.42% to 78.69%, 85.98%, and 87.27%, and high Ni ratio had higher deoxygenation capability and aromatic selectivity, simultaneously, it prone to creating material basis and spatiotemporal conditions for alkylation side reaction to increase C9 and above hydrocarbons. However, 1H NMR analysis confirmed that the main reaction of aromatization was still stronger than the side reaction even under high Ni ratio condition. Aromatics and coke production from acidic zeolite catalyzed reforming of oxygenates were competing reactions. In-situ catalysis of ternary cathodes produced more small molecule products to enter the inner pores of Ru/HZSM-5, forming more difficult to remove microporous coke, and the effect of increased Ni ratio was more obvious, but coke content reduced from 4.51% to 4.11%, 4.13%, and 3.05%, respectively.

Sulfurous zeosils for dehydra-decyclization of tetrahydrofuran to renewable butadiene

Renewable 1,3-butadiene (1,3-BD, C4H6) was synthesized from the tandem decyclization and dehydration of biomass-derived tetrahydrofuran (THF) on weak Brønsted acid zeolite catalysts.

Recent modifications of MCM-22 and MOR zeolite in MTO reaction: A review

Since the discovery of the Methanol-to-Olefins (MTO) process as a sustainable and nonpetroleum method for generating light olefins, there has been a growing interest in the utilization of acidic zeolite catalysts. In this review, we highlighted the application and modification of MCM-22 and MOR zeolite catalysts, shedding light on their distinctive properties and the ongoing endeavors to optimize their catalytic performance. Notably, the choice of catalyst and specific modifications significantly influence the outcomes of light olefin selectivity, propylene-to-ethylene (P/E) ratios, and catalytic lifetime. This research offers insights into the current status of research on MCM-22 and MOR zeolites and imparts a valuable understanding of the developments of both catalysts in this crucial catalytic field.

Heteroatom Lewis acid zeolites: synthesis, characterization and application in the conversion of biomass-derived oxygenates

This review summarizes recent advances in the synthesis, characterization and application of heteroatom (Ti, Zr, Sn, and Hf) Lewis acid zeolites in the conversion of biomass-derived oxygenates.

Fine Tuning of Hierarchical Zeolite Beta Acid Sites Strength

Two different synthesis methods to obtain hierarchical Beta zeolite are investigated: direct synthesis using cetyltrimethylammonium bromide (CTAB) as a mesoporous template and post-synthesis desilication by etching with NaOH and TPAOH. The main focus of this study is to show the possibility of fine tuning of the acid site (OH) strength (Brønsted and Lewis acid sites) through wet impregnation of these hierarchical Beta zeolites with divalent metal cations (Mg2+, Co2+, Ni2+, Cu2+, and Zn2+), which are important for various applications. Fourier transform infrared spectroscopy (FTIR) and deuterated acetonitrile as the probe molecule were used as a powerful technique to analyze the quantity and number of Brønsted/Lewis acid sites in the modified zeolite Beta structure. Investigating the influence of different divalent metal cations with a comparable ionic radius on the acidity of the hierarchical Beta zeolites, the present research aims to shed light on the structure–activity relationship that determines their catalytic behavior, for the development of efficient and environmentally friendly catalysts for various industrial applications.

Ionothermal synthesis of ZSM-5/AlPO4-5 composite zeolites and their catalytic performances in the methanol-to-olefin reaction

Composite zeolites, specifically ZSM-5/AlPO4-5 ([E]-Z5/Al5, [B]-Z5/Al5 and [H]-Z5/Al5), were prepared using tri-substituted imidazolium bromide ionic liquids (ILs). The ILs used were 1-ethyl-2,3-dimethylimidazolium bromide ([EMMIM]Br), 1-butyl-2,3-dimethylimidazolium bromide ([BMMIM]Br) and 1-hexyl-2,3-dimethylimidazolium bromide ([HMMIM]Br). The structure, morphology and acidity of the composite zeolites were analyzed using various techniques, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR), N2 isothermal adsorption-desorption, thermogravimetric analysis (TGA), temperature-programmed desorption of ammonia (NH3-TPD) and nuclear magnetic resonance spectroscopy (NMR). The catalysts obtained demonstrate outstanding performance in the methanol-to-olefin (MTO) reaction, with a catalytic lifetime extended by approximately tenfold and an approximately 10 % increase in the yield of light carbon olefins compared to the traditional hydrothermal Z5/Al5 catalyst. There is a strong relationship between the selectivity and stability of the MTO reaction with the optimized grain size and catalyst acidity.

Simulating Crystal Structure, Acidity, Proton Distribution, and IR Spectra of Acid Zeolite HSAPO-34: A High Accuracy Study.

It is a challenge to characterize the acid properties of microporous materials in either experiments or theory. This study presents the crystal structure, acid site, acid strength, proton siting, and IR spectra of HSAPO-34 from the SCAN + rVV10 method. The results indicate: the crystal structures of various acid sites of HSAPO-34 deviate from the space group of R3¯; the acid strength inferred from the DPE value likely decreases with the proton binding sites at O(2), O(4), O(1),and O(3), contrary to the stability order in view of the internal energy; the calculated ensemble-averaged DPE is about 1525 kJ/mol at 673.15 K; and the proton siting and the proton distribution are distinctly influenced by the temperature: at low temperatures, the proton is predominantly located at O(3), while it prefers O(2) at high temperatures, and the proton at O(4) assumedly has the least distribution at 273.15-773.15 K. In line with the neutron diffraction experiment, a correction factor of 0.979 is needed to correct for the calculated hydroxyl stretching vibration (ν(O-H)) of HSAPO-34. It seems that the SCAN meta-GGA method, compensating for some drawbacks of the GGA method, could provide satisfying results regarding the acid properties of HSAPO-34.

Monitoring of Chemical and Fermentative Characteristics during Different Treatments of Grape Pomace Silage

Grape pomace is a fibrous food with satisfactory quantities of residual sugars. It meets the desirable characteristics for conservation in the form of silage for later use in animal feed, mainly for ruminant herbivores. Fresh grape pomace was subdivided into three treatment groups: grape pomace as a control, grape pomace treated with an inoculum of lactic acid bacteria, and grape pomace treated with zeolite. The treatments were performed in micro-silos over 90 days. There was a significant change (p < 0.05) in the chemical characteristics, content of biologically active compounds, and fermentative characteristics during the silage of all treatments. After 30, 60 and 90 days of ensiling, silages treated with inoculum and zeolite had better fermentation quality indicated by significantly (p < 0.05) lower pH and ammonia-nitrogen contents compared with those of the control. Also, the additives have decreased the total polyphenols and tannins for 97% in average which confirmed that lactic acid bacteria and zeolite positively effect on the degradation of polyphenols and tannins in grape pomace silage. The Flieg score was calculated and the values were above 80% what refers to excellent silage. In conclusion, our results suggest that inoculant and zeolite supplementation improves the quality of grape pomace silage for later use in animal feed.

Ketonization of propionic acid over TS-1 and Ti-Beta zeolites: Mechanism and effects of topology and hydrophobicity

Ketonization of propionic acid has been investigated on Lewis acidic TS-1 and Ti-Beta zeolites to understand the reaction mechanism and effects of pore topology and hydrophobicity. Characterizations showed that TS-1 and Ti-Beta (Si/Ti = 40) exhibited a similar acidity whereas TS-1 was more hydrophobic than the silanol-rich Ti-Beta. TS-1 showed higher activity, selectivity, stability and was more resistance to H2O than Ti-Beta. A combination of infrared spectroscopic, isotopic and kinetic studies showed that the molecularly adsorbed monodentate propionic acid is the most abundant reactive intermediate, and C-C coupling is the rate-determining step. The mechanism of ketonization of propionic acid at isolated tetrahedral Ti centers can be described by a Langmuir-Hinshelwood model. The turnover rate on TS-1-40 is ∼ 1.3 times higher than that on Ti-Beta-40, which is consistent with the lower fitted free activation energy, i.e., the energy difference between C-C coupling transition state and two co-adsorbed propionic acids at a Ti center. The slightly lower activation enthalpy on Ti-Beta-40 than TS-1-40 is over-compensated by much larger entropy penalty, due to more silanol groups and hydrogen bonded propionic acids in close proximity to the Ti center for Ti-Beta-40, which impose additional steric hindrance to bulkier C-C coupling complex at transition state and outweigh the difference of steric hindrance of pore confinement between MFI and BEA frameworks. This work provides insight into the ketonization mechanism on Lewis acidic zeolites, and indicates that moderate pore size with hydrophobic property promotes ketonization of carboxylic acid at isolated tetrahedral Ti centers confined in zeolites.

Tuning the acidity of SAPO-34 zeolite through niobium incorporation for enhanced catalytic performance during MTO reaction

SAPO-34 zeolite is commonly used for light olefin production, an important petrochemical, through the methanol-to-olefin (MTO) conversion process. To modify the physicochemical characteristics of the SAPO-34 zeolite, a series of Nb-incorporated SAPO-34 catalysts were synthesized to alter the crystal size and acidity of the catalysts to enhance its MTO catalytic properties. The Nb incorporation reduced crystal size from 4.6 μm to 1.4 μm, with enhanced acidity for the Nb0.005SP catalyst. The catalytic results revealed that the Nb0.005SP catalyst showed remarkably superior MTO conversions, ∼2.5 time as compared with conventional SP catalyst, due to its reduced crystal size, higher surface area and higher acid sites concentration owing to its shorter diffusion pathlength, greater number of exposed active sites and ability to maintain MTO reaction for longer time, respectively. Moreover, the Nb0.005SP catalyst also exhibited a lower hydrogen transfer index-HTI index with a slight slope, leading to slower coking, enhanced light olefine selectivity and a longer lifetime compared to other counterparts.

Effect of the Structure and Acidity of Zeolites on the Synthesis of Solketal from Glycerol and Acetone

Effect of the Structure and Acidity of Zeolites on the Synthesis of Solketal from Glycerol and Acetone

Kinetic, Spectroscopic, and Theoretical Study of Toluene Alkylation with Ethylene on Acidic Mordenite Zeolite

Kinetic, Spectroscopic, and Theoretical Study of Toluene Alkylation with Ethylene on Acidic Mordenite Zeolite