Acid Site Density Research Articles

Conversion of Sugar Di-Ketals to Bio-Hydrocarbons through Catalytic Cracking over Beta Catalysts in Fixed and Fluidized Catalytic Beds

Second-generation biomass (BM) can be produced in amounts that meet worldwide fuel demands. However, BM favors parallel and undesirable reactions in its transformation chain. We circumvent this problem by first modifying BM by ketalization, giving a user-friendly liquid we named BP (bio-petroleum). This study converted a representative compound of BP, DX (1,2:3,5-di-O-isopropylidene-α-D-xylofuranose), mixed with n-hexane by beta zeolites and catalysts containing beta zeolite. Beta zeolite showed low coke and high liquid product yields in converting this mixture (having 30 wt. % DX) into hydrocarbons in a fixed-bed reactor at 500 °C with a space velocity of 16 h−1 (0.3 catalyst/feed). Its performance was further improved by steam treatment (lowering the coke yield by lowering the acid site density) or incorporation into a catalyst (improving DX participation due to the active sites in the matrix). Further, by changing the conversion process from a fixed bed to a fluidized cracking unit, a much larger amount of the deactivated catalyst could be used (catalyst/feed = 3), remarkably reducing oxygenates and fully converting DX. Additionally, the green hydrocarbon efficiency (olefin, aromatics, furans, and cyclo-alkanes) of DX was approximately 77%. Hence, beta catalysts were shown to have a great potential to provide green fuels for future bio-refineries.

Green catalyst access to thieno [2, 3‐b] pyridines derivatives

AbstractThe current study focuses on the use of tungstovanadophosphoric heteropoly acid H4PW11VO40·8 H2O (PVW) with Keggin structure and supported on acid activated (PVW/AAM) in the synthesis of new substituted Thieno [2, 3‐b] pyridines derivatives. The suggested protocol is an easy, environmentally friendly method for synthesis of thieno [2,3‐b] pyrimidine derivatives obtained from 3‐cyano‐2‐aminothiophene as building blocks under solvent‐free reactions condition. Excellent product yields of substituted Thieno [2, 3‐b] pyridine derivatives (60%–97%) were achieved using the synthesized PVW/AAM catalyst. The current processes provide benefits including a quicker reaction time, an easy set‐up, and high yields. Spectroscopic data (IR, +H and 13C NMR spectra) have revealed the structural details of all target compounds. The catalyst was characterized by X‐ray diffraction, BET and Fourier‐transformed infrared spectroscopy. X‐ray diffraction showed that PVW was correctly incorporated on an acid activated clays support. In comparison to the parent, Tungstovanadophosphoric acid, the PVW supported acid activated montmorillonite provided increased Lewis acid site density, redox characteristics, and surface area. Due to the recoverability of heterogeneous catalysts, the heterogenization of homogeneous catalysts is very attractive. In addition, the produced catalysts can be simply removed from the reaction system and reused six times more effectively.

Influence of Brønsted Acid-Site Density on Reaction-Diffusion Phenomena that Govern Propene Oligomerization Rate and Selectivity in MFI Zeolites

Brønsted acid zeolites catalyze propene oligomerization to higher-molecular-weight alkenes. Previous studies that only consider kinetic factors have reached contradictory conclusions regarding the dependence of oligomerization rates on H+-site density in MFI zeolites. Herein, we account for both the reaction and diffusion phenomena that govern the rates and selectivity of propene oligomerization and interrogate suites of MFI samples synthesized with widely varying H+-site density (0.3–5.7 H+/unit cell; Si/Al 13–250) and crystallite size (0.03–2.65 μm). Heavier alkene products become occluded within zeolitic micropores during reaction and impose intrazeolite diffusional restrictions for all MFI samples over wide ranges of reaction conditions (483–523 K, 7–615 kPa C3H6). This occluded organic phase becomes heavier in composition at higher propene pressures and lower reaction temperatures, which favor the growth of higher-molecular-weight oligomers, resulting in effective diffusivities of propene and product alkenes that systematically decrease with increasing propene pressure. Analysis of product selectivity reveals that MFI samples of lower H+-site density possess higher rate constant ratios for trimerization relative to dimerization, leading to the formation of heavier alkenes within their micropores and, in turn, to a greater decrease in the effective diffusivity of propene and product alkenes with increasing propene pressure. As a result, measured dimerization rates on MFI samples, which convolve the influences of kinetic factors and intrazeolite diffusional constraints imposed by the occluded organic phase, exhibit an increasingly negative-order dependence on propene pressure with decreasing H+-site density. The combined influences of kinetic factors and intrazeolite diffusional constraints result in different dependences of oligomerization rate on H+-site density when measured at different propene pressures, reconciling apparent contradictions among previous reports. Overall, these findings reveal the strong influences of H+-site density in MFI zeolites on both the kinetics of propene oligomerization reactions and the composition of the product-derived intrazeolite organic phase that influences effective diffusivities, and consequently measured propene oligomerization rates and product selectivity.

Ethanol Conversion Catalyzed by MCM-22 and Its Dealuminated and Delaminated Forms

The conversion of ethanol into hydrocarbons, particularly into light olefins, was studied over MCM-22 zeolite in their acid form (HMCM-22) and its derived forms obtained by dealumination with oxalic acid (HMCM-22(OA)) and delamination (HITQ-2). The treatment with oxalic acid did not affect zeolite textural properties but reduced the total density and strength of the acid sites. As to the delamination process, HITQ-2 zeolite presented the highest Brunauer, Emmett and Teller (BET) specific area, mesopore volume, and external area, but the microporosity was not affected. This sample showed a lower SiO2/Al2O3 ratio than the precursor HMCM-22, resulting in the highest acid site density but with the predominance of acid sites with weak and intermediate strength. Both dealumination and delamination led to an increase in the number of structural defects in the samples. The comparison of the catalytic performance at 500 ºC showed that despite the differences in the acidic and textural properties of the samples, they were active for ethanol conversion and highly selective for ethylene production. Ethanol conversion, followed by in situ diffuse reflectance spectroscopy (DRIFTS), was also investigated. It showed that, for both samples, the “coke band” intensity was already significant after 1 min of reaction, similar to what was detected for HMCM-22.

Optimizing lactic acid production for agricultural wastes revalorization via sugars hydrothermal conversion with zirconia-based catalysts: response surface methodology

The hydrothermal conversion of a complex sugars solution comprising glucose, arabinose, and xylose with zirconia-based catalysts to produce lactic acid (LA) was studied. Catalysts were synthesized by a simple template-assisted sol–gel method. Alternative template removal procedures, such as refluxing ethanol extraction, were compared to the conventional direct calcination. The catalyst obtained after ethanol extraction (Z-Ex) reported the highest specific surface area (323 m2 g−1), total pore volume (0.21 cm3 g−1) and density of acid sites (1.111 µmol m−2), with a significant contribution of strong acid sites. On the other hand, template removal by thermal treatment transformed the hydrous zirconia into crystalline tetragonal phase, reducing the specific surface area and removing most of the acid sites. Catalytic tests were carried out in a stirred batch reactor, resulting Z-Ex the most selective towards LA production. A four-factor experimental design was performed for Z-Ex catalyst by varying temperature, reaction time, initial pressure, and catalyst/reactants ratio. Results were analyzed using the response surface methodology (RSM) to maximize the LA production. A molar yield of 61.2% towards LA and complete sugars conversion were reached at optimized operating conditions: 189 °C, 208 min, 0.5 g catalyst g−1 reactants, and 10 bar N2. Additionally, fitting models for main by-products molar yields (furans, glyceraldehyde, glycolic, formic, acetic, and levulinic acids) were obtained with good accuracy prediction. All responses were jointly studied to understand the reaction mechanisms involved in generation of intermediaries and undesired degradation products.Graphical Abstract

Cooperative catalytic effects between the penta-coordinated Al and Al2O3 in Al2O3-AlPO4 for aldol condensation of methyl acetate with formaldehyde to methyl acrylate

The bare amorphous Al 2 O 3 -AlPO 4 and Cs/Al 2 O 3 -AlPO 4 catalysts were developed for the aldol condensation of methyl acetate with formaldehyde to methyl acrylate. The structure and property of catalyst were characterized by XRD, XPS, BET, Pyridine-IR, FT-IR, 27 Al-MASNMR, NH 3 -/CO 2 -TPD and SEM. The correlation between structural features and acid-base properties was established, and the loading effect of the cesium species was investigated. Due to cooperative catalytic effects between the penta-coordinated Al and Al 2 O 3 , the weak-Ⅱ acid and medium acid site densities and the product selectivity were improved. While the basic site densities of these catalysts were almost in proportion to the conversion of methyl acetate. The loaded Cs could form new basic sites and change the distribution of acid sites which further enhance the catalytic performance. As a result, the 10Cs/8AlP was proved to be an optimal catalyst with the yield and selectivity of 21.2% and 85% for methyl acrylate respectively. During the reaction, a deactivation behavior was observed on 10Cs/8AlP catalyst due to the carbon deposition, however, it could be regenerated by thermal treatment in the air atmosphere at 400 °C.

Acid Site Density as a Kinetic Descriptor of Catalytic Reactions over Zeolites

A mathematical framework for the quantitative description of site density dependence of catalytic data (activity and selectivity) was developed considering that changes in the electrostatic contribution to the Gibbs energy of an elementary reaction on the acid sites in zeolites depend on the proximity of these sites. For the two-step sequence with the most abundant surface intermediate, an expression for turnover frequency explicitly containing the acid site density was derived. The treatment was extended to linear sequences of elementary reaction and analysis of the acid site density on selectivity in parallel and consecutive reactions, allowing to quantitatively relate the ratio between products for such reactions. Experimental data on Prins condensation of isopulegol with acetone and transformations of syngas over mesoporous H-ZSM-5 supported cobalt nanoparticles to a mixture of iso- and normal hydrocarbons were used as a show case.

Silica-Resin-Bentonite Nanocomposite and Its Application in Catalysis

Bentonites are natural clays found in abundance in deposits all over the planet and possess certain properties that make them interesting for various industrial applications. Through their activation or acid treatment, they can be used as catalysts in several reactions of interest. However, these materials form colloidal suspensions in water or in aqueous solutions, which makes their separation and recovery difficult and prevents their implementation on an industrial scale. To overcome these limitations, in the present work, a silica-resin-bentonite composite material was synthesized and activated with HNO3. The activated solids were characterized and evaluated in the catalytic reaction of solketal synthesis from glycerol and acetone. The best results were obtained for a composite containing 47 wt.% acidified bentonite at 90 °C, with a HNO3 concentration of 0.5 mol L−1, which was attributed to both its acid site density—3.9 mmol per gram of bentonite—and the acidic strength of these sites.

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

Isolated Fe(III) and Cr(III) sites contained in nanoporous voids of isoreticular carboxylate MIL-101(Fe) and MIL-101(Cr) are interrogated for their reactivity and selectivity of liquid-phase styrene oxidation by hydrogen peroxide (H2O2). Batch kinetic measurements in acetonitrile (MeCN) at 323 K showcase that both metal-normalized oxygenate production and H2O2 consumption rates are O(101) higher for MIL-101(Fe) than MIL-101(Cr). Thermodynamically consistent reaction pathways, constructed through spiking experiments, reveal complex interconnectivities between primary (styrene oxide, benzaldehyde) and secondary (styrene glycol, benzoic acid, phenylacetaldehyde) oxygenates. Though benzaldehyde is the majority product for both MIL-101(Fe) and MIL-101(Cr), isoconversion (Xstyrene = 7%) product distributions suggest intrinsic differences in preferred reaction pathways. Apparent energy barriers for all pathways are lower over MIL-101(Fe) than for MIL-101(Cr), conferred by metal electron affinity differences for primary oxygenate selectivity, while secondary (inter)conversion rates trend with acid site densities. Fitted rate laws, radical trapping, adsorption experiments, and complementary DFT calculations indicate surface-mediated reactions by H2O2-derived surface species that outcompete bound styrene, product oxygenate, solvent, and water molecules for both MIL-101(Fe) and MIL-101(Cr) in MeCN. Extracted enthalpic and entropic effects from temperature-dependent experiments (318–328 K) in MeCN and MeOH showcase the ability of hydrogen bonding solvents in locally hydrophilic environments to selectively stabilize primary oxygenate transition states and indicate additional confinement effects from microporous substructures in MIL-101(Fe) and MIL-101(Cr). Simplified rate expressions are expanded to encompass first-order catalyst deactivation rates through temporal metal leaching experiments and assert that metal leaching dominates MIL-101(Cr) catalyst inefficiencies, while a combination of metal leaching and other (ir)reversible site changes are present for MIL-101(Fe). Overall, this work combines kinetic, spectroscopic, numerical, and computational approaches to rigorously define reaction and deactivation mechanisms for styrene oxidation by H2O2 over isoreticular MIL-101(Fe) and MIL-101(Cr).

Construction of Acylamide-functionalized MOFs for efficient catalysis on the conversion of CO2

By employing a C3-symmetric ligand, 3,3′,3′'-[1,3,5-benzenetriyltris- (carbonylimino)]tris-benzoic acid (H3L), three metal-organic frameworks formulated as {Na4[Zn3(L)2(µ3-OH)(µ2-OH)3]·3DMF}n (1), {[Ca2(L)(MeOH)2(DMF)3]·Cl}n (2) and [Sr2(L)(H2O)2(DMF)Cl]n (3) have been solvothermally synthesized and structurally characterized by IR, PXRD and X-ray single crystal diffraction analyses. Complex 1 features a 2D twofold interpenetrated structure in which the [Zn3(µ3-OH)(µ2-OH)3(CO2)3O3] subunit acts as a 6-connected node and the L3− ligand as a 3-connected node, exhibiting a binodal (3, 6)-connected topology with a {43}2{43.612} point symbol. Complex 2 shows a 2D double-layered structure, exhibiting a (3,6)-connected {43}2{46.66.83} topology based on a centrosymmetric tetranuclear [Ca4(CO2)6] subunit as a 6-connected node and the L3− ligand as a 3-connected node. Complex 3 exhibits an extended 3D framework with a {46}2{412.612.84} topology in which the centrosymmetric {Sr4(CO2)6 [(O^O)acylamide]2} subunit performs as an eight connected node and the L3− ligand as an unusual 4-connected node. Complex 1 is explored well as a catalyst for the cycloaddition reaction of CO2 with epoxides into cyclic carbonates under the reaction conditions of 70°C, 1 bar atmosphere and free solvent. The efficient catalytic ability of 1 perhaps attributes to the high density of Lewis acidic sites of Zn2+ and Lewis basic -NH- groups in 1. Beside the basic function, the -NH- group in 1 can also perform as hydrogen bond donor (HBD) for the activation of epoxide in the catalytic process. A plausible mechanism for synergistic catalysis is proposed for the cycloaddition reaction.

The role and performance of isolated zirconia sites on mesoporous silica for aldol condensation of furfural with acetone

Furfural is an important bio-based platform chemical in the production of valuable products such as biofuel intermediates and polymeric materials. In this work, isolated Zr on mesoporous silica catalysts at varied Zr loading were prepared and evaluated for aldol condensation of furfural with acetone to 4-(2-furyl)− 3-buten-2-one(FAc) and 1,5-bis-(2-furanyl)− 1,4-pentadien-3-one(F2Ac). A remarkable effect of the Zr loading on the catalyst performance is revealed. The catalysts are characterized by XRD, BET, NH3-TPD, Py-FTIR, XPS, UV–visible, and TGA. The connectivity of Zr was characterized by XPS and UV–visible spectroscopy. For the 25 wt% Zr loading, Zr is present predominantly as isolated monomeric species on mesoporous SiO2. The types and densities of different acid sites of the catalysts are measured with Py-FTIR analysis. The results show that isolated Zr on mesoporous SiO2 enhanced Lewis acid site densities and exhibited superior catalytic activity for aldol condensation between furfural and acetone to produce FAc and F2Ac.

Insight into induction period of methanol conversion reaction: Reactivity of ethene-precursors over H-ZSM-5 zeolite is independent of Brϕnsted acid site density

A series of H-ZSM-5 (TZ-m, m represents different Si/Al ratios) has been prepared and their Methanol to Olefin (MTO) performance are investigated. By adjusting the catalyst weight of H-ZSM-5 loaded in the pulse micro-reactor, the total Brϕnsted acid sites (BAS) amount of TZ-m catalysts is unified. The resultant similar methanol conversion (∼24 %) over different TZ-m zeolites confirms that the MTO reaction is dominantly catalyzed by BAS. Nevertheless, the BAS density considerably influences the reaction pathways; more condensed BAS enhances the relative propagation of aromatic-based cycle to alkene-based cycle, and vice versa. However, isotopic co-feeding and switching experiment reveals that the reactivity of aromatic hydrocarbon pool (HCP) species, which has been considered as main ethene precursors, is almost independent of acid site density. Although large amounts of aromatics are generated via hydrogen transfer reactions on the sample with high acid site density, most of the confined aromatics function as coke precursors instead of active HCPs. The accumulation of such confined aromatics in zeolite channels further limits olefins mobility and their access to BAS, leading to decreased reactivity of alkene HCPs on high acid site-density samples.

Conversion of sugar diacetyls to bio-hydrocarbons by the catalytic cracking in a fixed bed with fresh and deactivated Beta zeolite

The conversion of biomass into fuel under typical refinery conditions is a promising solution to decrease carbon footprint. Herein we convert a representative compound of a new bio-petroleum, DX (1,2:3,5-di-O-isopropylidene-α-D-xylofuranose) mixture with n-hexane. Firstly fresh zeolites (Beta, ZSM-5 and USY) were explored. Beta zeolite showed a high performance in converting DX into hydrocarbons. Thus it was further modified by hydrothermal deactivation. This treatment reduced the acid site density of Beta, resulting in an improvement in aromatics, reducing gas 2-fold and coke 1-fold, and only leaving a small amount of oxygenates in the liquid fraction in the test with 20% DX.

Alkylation of isobutane with trans-2-butene on hydrothermally prepared BEA-type zeolitic materials with different crystallization time

It is widely known that hydrofluoric and sulfuric acids are the conventional catalysts used in the alkylation reaction, an important petrochemical process in the production of automotive fuels. However, these inorganic acids are highly toxic and therefore, solid zeolitic catalysts have emerged as an environmentally friendly alternative. In this work, a series of BEA-type zeolitic materials were prepared in hydrothermal systems varying the crystallization time to test their catalytic performance in the alkylation of isobutane with trans-2-butene. The materials were characterized by Infrared Spectroscopy (FT-IR), X-ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM), N2 physisorption, and total acidity measurements by ammonia method. The synthesis of BEA zeolite was successfully carried out at crystallization times between 8 and 20 h (ZB-8, ZB-12, and ZB-20 samples), whilst longer periods produce a combination of BEA and MFI zeolites (ZB-28 and ZB-96 samples). Based on the XRPD analysis, the possible presence of two polymorphs of the BEA zeolite is proposed. The synthesized materials in the acidic form were catalytically examined for 120 min at different contact times (0.078, 0.156, and 0.234 gcat × min × mol−1) and temperatures (40 and 60 °C). The reaction was fitted to second-order deactivation kinetics. High selectivity was observed for the group of C7-C9+ compounds in the steady-state condition, particularly towards the fraction of C8 compounds. The generation of the compounds that make up the alkylate group was favored in most catalytic tests. The highest yields for alkylate were achieved under conditions of 0.156 gcat × min × mol−1 and 40 °C with values of 9.5 and 12 % for the ZB-12 and ZB-96 catalysts, respectively. This study supported the importance of balancing the density of acidic sites and the porous topology of zeolitic materials in conjunction with the selection of reaction parameters such as temperature and contact time to favor the yield towards alkylate.

Kinetic studies on the extraction of oil from a new feedstock (Chukrasia tabularis L. seed) for biodiesel production using a heterogeneous catalyst.

This study has identified a new feedstock Chukrasia tabularis L. (C. tabularis) seed for the production of biodiesel. Oil was extracted from the seeds with and without autoclave-assisted ultrasonic homogenization (AUH) pretreatment using different solvents. The solvent n-hexane with AUH pretreatment yielded a maximum oil yield of 32 wt%. The kinetics and thermodynamics of the extraction process were studied in a batch. The data showed that extraction followed first-order kinetics with a rate constant of 1.4 × 10-4min-1, activation energy of 63.604kJmol-1 and pre-exponential factors of 66.66 × 104s-1. The physiochemical properties of the oil were determined from which it was identified that C. tabularis oil has high free fatty acid (FFA) content, requiring a single-step esterification cum transesterification reaction to produce biodiesel economically. The modified aryl diazonium salt reduction process was used to synthesize a heterogeneous acid catalyst (HAC) from activated carbon precursor and was used to catalyze biodiesel reaction. Furthermore, HAC was characterized by different analytical techniques and it was found that it had an acid site density of 1.02mmolg-1 and a specific surface area of 602 m2g-1. The parameters affecting the biodiesel process were studied to obtain a maximum biodiesel conversion of 98.5% at 6 wt% catalyst loading, 15:1 methanol to oil molar ratio, 120min reaction time, 70 ºC reaction temperature, and 500rpm stirring rate. Reusability studies were performed which showed that HAC can be recycled up to five cycles with a conversion above 90% in the fifth cycle. Moreover, the fuel properties of biodiesel were determined using standard methods and were compared with ASTM D6751 and EN14241 standards.

Oxidation reaction mechanism of hydrothermal carbon microspheres with applications to transesterification after sulfonation

AbstractBackgroundAn efficient sulfonic acid‐type acid catalyst with high acid site density based on hydrothermal carbon microspheres (HCMs) has been developed. The reaction by which double bonds in the HCMs were oxidized to generate carboxyl groups was evaluated based on density functional theory calculations.ResultsSulfonic acid‐type HCMs (SHCMs) were prepared from HCMs through a three‐step process comprising oxidation, amidation and sulfonation. An analysis of the oxidation process indicated that the formation of carboxyl groups involved the activation of O2 molecules and CH bonds, the cleavage of CC bonds, the homolytic fission of peroxy acids and the coupling reactions of H• radicals. The formation of numerous carboxyl groups on the HCM surfaces was the key to obtaining SHCMs with a high acid density of 14.5 mmol g−1.ConclusionsThe SHCMs obtained exhibited good catalytic performance during the transesterification of waste frying oil with methanol. Reactions performed using a methanol/oil molar ratio of 9:1 at 90 °C for 5 h gave a fatty acid methyl ester yield of 85.56%. © 2022 Society of Chemical Industry (SCI).

Synthesis, characterization, modeling and catalytic testing of tungstated zirconia supported Ni catalysts for Hydrodeoxygenation of Guaiacol

Tungstated zirconia supported Ni catalysts with different Ni contents (3 to 20 of % w/w) were synthesized at mild conditions in a stirred pressure reactor. We reported multi-objective optimization (MOO) of tungstated zirconia preparation in terms of Brønsted acid site density and surface area for the first time in the open literature. Optimization of nickel content was also performed in terms of HDO activity and selectivity. Obtained MOO results showed that optimum nickel content was 15% in terms of selectivity and activity. Predicted response results were in good agreement with the experimental response results. The catalytic performance of the catalyst samples was tested on the HDO reaction of guaiacol. Additionally, an HDO mechanism for Ni-doped WOxZrO2 catalyzed guaiacol conversion was proposed. High activity and selectivity rates were achieved during the experiments and cyclohexane was obtained as a main product in the presence of more than 10% of Ni-doped tungstated zirconia catalyst.

Effect of thermal treatment on K3PW12O40 for cyclohexene oxidation reaction to adipic acid

The use of heteropolysalts in the cyclohexene oxidation reaction has shown good results, but there is still a significant solubility of this catalyst in the aqueous phase of the reaction medium which is not discussed in most articles dealing with this subject. A thermal treatment, such as calcination step, can significantly affect the properties of a catalyst, including its solubility, sedimentation and acidity. These effects are very important in batch reaction processes and frequently neglected. Thus, the main objective of this work was to study the effect of different calcination temperatures (200 and 600 °C) on the solubility and the acidity of Keggin-type catalysts (K3PW12O40). In addition, the effect of reaction temperature (65, 75 and 85 °C) on the conversion and distribution of products in the oxidation of cyclohexene with these two catalysts was analyzed. The heteropolysalts were characterized using XRD, Raman spectroscopy, N2 physisorption, SEM-EDS, acid-base titration and NH3-TPD. XRD and Raman results showed that the catalysts synthesis was carried out successfully and the thermal treatments did not affect the polyanion structures, even at the highest temperature (600 °C). When compared to the catalyst treated at 600 °C, the KPW-200 catalyst showed greater solubility in the reaction medium. However, it achieved 100% conversion and the highest yield of adipic acid (89%) at 75 °C, in addition to the highest density of acid sites. Tests were performed using the aqueous phase of the post-reaction solution to evaluate the occurrence of homogeneous catalysis under the same conditions. The results showed that, despite the solubilization of the catalyst, there was no adipic acid formation, only of intermediate compounds. Thus, the contribution of homogeneous catalysis in the synthesis of adipic acid is discarded, and the acidity of the catalyst seems to be the determining parameter in the formation of this product. Acidity can influence both the oxidation and hydrolysis steps present in the reaction mechanism and can justify these results.

Investigate the equivalent weight effect on properties of perfluorosulfonic acid membrane in concentrated electrolytes

In this contribution, a series of characterizations, such as water uptake, acid uptake, membrane density, and conductivity measurements, have been utilized to study the effect of equivalent weights (EW) on ion partitioning and transport behavior of perfluorosulfonic acid membranes produced by 3M Corp. It is observed that water sorption and acid uptake both increase with a decrease in EW. This phenomenon results from a higher sulfonic acid site density in the membrane with a lower EW. Just as important, the Donnan potential opposing co-ion uptake on the membrane surface decreases with decreasing equivalent weight. The membrane with a lower EW is found to have a higher membrane density at the same water content, but the porosity does not show a large discrepancy among the three membranes we studied. Even though the higher acid concentration in membranes results in lower activity coefficients of ions, its higher water content still facilitates faster proton mobility and higher ion conductivity. This analysis helps draw a picture of the relationship between membrane morphology and dynamics of PFSA membranes.

Insights into structure–performance relationship in the catalytic cracking of high density polyethylene

Zeolite is considered a promising catalyst for plastic cracking because of its well-defined acid sites, high product selectivity, and outstanding stability. The relationship between zeolite structure and catalytic performance is still not well understood. Therefore, on either as prepared or purposely modified ZSM-5 zeolites, we made a systematic investigation of how acid density and pore structure affect catalytic performance in this work. Our results demonstrate that Brønsted acid site density had profound impact on the catalyst lifetime and aromatic selectivity. The relationship between Brønsted acid site density and catalyst lifetime displays a tendency that catalyst lifetime declines with acid site density at the beginning, then rises up, instead of a linear correlation. Also, the increase of mesoporosity extends the catalyst lifetime to some extent. This information can give us a better understanding of how to design higher-performance catalysts for chemical upcycling of waste plastics.