Acid Catalyst Research Articles

Sulfonated carbon–based heterogeneous acid catalysts in direct biomass redox flow fuel cell: A review

AbstractThis review focused on the potential applications of sulfonated carbon–based heterogeneous acid catalysts for the hydrolysis of lignocellulosic biomass (LCB) fuel feedstock and the development of membrane electrode assembly (MEA) for the direct biomass redox flow fuel cell (DBRFFC). LCBs are hydrolysed to yield simple sugars, which are subsequently oxidized over catalysts in the anode tank of the DBRFFC to generate electricity. Ferric chloride used as a catalyst in the DBRFFC is not efficient for glucose production from LCB, such that the power performance of the DBRFFC is affected during glucose oxidation due to low glucose yield from LCB for electron generation. Sulfonated carbon–based solid acid catalysts (SCSACs) have been established as efficient catalysts for the hydrolysis of LCB and as metal catalyst supports for the fabrication of MEA for further oxidation of glucose and its oxidation by‐products. These capabilities of SCSACs can be explored and applied to significantly improve the power output of the DBRFFC through efficient hybrid catalyst design. There is still a scarcity of literature on this subject and their combination with ferric chloride to enhance glucose yield and oxidation in DBRFFC. This gap was filled by discussing the various types of sulfonated carbon–based catalysts, highlighting their synthesis routes, and their applications in organic compound synthesis, and membrane electrode development in DBRFFC. The knowledge derived will certainly be beneficial to researchers willing to improve the performance of DBRFFC through molecular catalyst design and electrode membrane development for application in DBRFFC.

Conversion of Used Cooking Oil into Biodiesel by Utilizing Zirconia Catalyst as Acid Catalyst (SO4/ZrO2) and Base Catalyst (ZrO2/CaO)

Conversion of Used Cooking Oil into Biodiesel by Utilizing Zirconia Catalyst as Acid Catalyst (SO4/ZrO2) and Base Catalyst (ZrO2/CaO)

Formation of Core‐Shell Ir@TiO2 Nanoparticles through Hydrogen Treatment as Acidic Oxygen Evolution Reaction Catalysts

Formation of Core‐Shell Ir@TiO₂ Nanoparticles through Hydrogen Treatment as Acidic Oxygen Evolution Reaction Catalysts

Enantioselective formal (3 + 3) cycloaddition of bicyclobutanes with nitrones enabled by asymmetric Lewis acid catalysis

The absence of catalytic asymmetric methods for synthesizing chiral (hetero)bicyclo[n.1.1]alkanes has hindered their application in new drug discovery. Here we demonstrate the achievability of an asymmetric polar cycloaddition of bicyclo[1.1.0]butane using a chiral Lewis acid catalyst and a bidentate chelating bicyclo[1.1.0]butane substrate, as exemplified by the current enantioselective formal (3 + 3) cycloaddition of bicyclo[1.1.0]butanes with nitrones. In addition to the diverse bicyclo[1.1.0]butanes incorporating an acyl imidazole group or an acyl pyrazole moiety, a wide array of nitrones are compatible with this Lewis acid catalysis, successfully assembling two congested quaternary carbon centers and a chiral aza-trisubstituted carbon center in the pharmaceutically important hetero-bicyclo[3.1.1]heptane product with up to 99% yield and >99% ee.

Formulation of a carbon-based solid acid catalyst from groundnut husk for the esterification of oleic acid

In this research, a biochar was prepared from groundnut husk and sulphuric acid. The biochar wassulphonated with chlorosulphonic acid to give a carbon-based sulphonated solid acid catalyst (SAC). The catalyst was characterised by N2 adsorption and desorption at 77K after degassing overnight under vacuum at 250˚ C, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and total acid density measurement. The results of the acid density measurement showed that the sulphonated biochar has a relatively high acid density of 3.2 mmol/g, while that of the non-sulphonated counterpart is 0.56 mmol/g. Comparison of the percentage conversion of oleic acid by esterification with methanol and butanol was carried out under three different conditions, viz: without catalyst, with the non-sulphonated biochar and with the sulphonated biochar, under the same experimental conditions of 5% catalyst weight percent (based on weight of acid), acid-methanol mole ratio of 1:12, reaction temperature of 70 oC, and five hours reaction time. Up to 91.6% percentage conversion of oleic acid to methyl oleate and 86.4% for butyl oleate were achieved, proving the effectiveness of the sulphonated biochar in catalysing the esterification reaction of oleic acid with methanol and butanol. The results of this study are expected to provide insights into the development of sustainable and cost-effective solid acid catalysts for the synthesis of oleate esters and other value-added materials from renewable feedstocks.

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.

Zeolite Catalysts for Selective Hydrocracking of Polycyclic Aromatic Hydrocarbons – Structures and Mechanisms

AbstractSelective hydrocracking of polycyclic aromatic hydrocarbons (PAHs) from heavy oils and tar to high‐value chemicals such as benzene, toluene, and xylene (BTX) is a promising technology. Due to the lack of comprehensive and rational understanding of the reaction mechanisms, the development and preparation of catalysts and the improvement of catalysis technology are rarely carried out. Since zeolites as crucial solid acid catalyst components in catalytic hydrocracking of PAHs are indispensable, this review systematically analyzed the mechanisms and research advances in hydrogenation, isomerization, and ring‐opening (cracking) on zeolite catalysts. Efficient zeolite catalysts for hydrocracking should have appropriate pore structures for the required diffusivity for reactants and products to avoid secondary polymerization and coke formation, an ideal distribution and strength of acid sites for the formation of the desired carbocation intermediates to achieve the selectivity of products and precisely tunable metal to acid functions to control the competition between (de)hydrogenation and ring‐opening reactions leading to the facilitation of the reaction mechanisms for the desired products. This poses challenges for the research and development of industrial relevant zeolite catalysts.

Simulation of the non-adiabatic dynamics of an enone-Lewis acid complex in an explicit solvent.

Unlocking the full potential of Lewis acid catalysis for photochemical transformations requires a comprehensive understanding of the ultrafast dynamics of substrate-Lewis acid complexes. In a previous article [Peschel et al., Angew. Chem. Int. Ed., 2021, 60, 10155], time-resolved spectroscopy supported by static calculations revealed that the Lewis acid remains attached during the relaxation of the model complex cyclohexenone-BF3. In contrast to the experimental observation, surface-hopping dynamics in the gas phase predicted ultrafast heterolytic dissociation. We attributed the discrepancy to missing solvent interactions. Thus, in this work, we present an interface between the SHARC and FermiONs++ program packages, which enables us to investigate the ultrafast dynamics of cyclohexenone-BF3 in an explicit solvent environment. Our simulations demonstrate that the solvent prevents the dissociation of the complex, leading to an intriguing dissociation-reassociation mechanism. Comparing the dynamics with and without triplet states highlights their role in the relaxation process and shows that the Lewis acid inhibits intersystem crossing. These findings provide a clear picture of the relaxation process, which may aid in designing future Lewis acid catalysts for photochemical applications. They underscore that an explicit solvent model is required to describe relaxation processes in weakly bound states, as energy transfer to the solvent is crucial for the system to reach its minimum geometries.

Surface-Activated Mechano-Catalysis for Ambient Conversion of Plastic Waste.

Improved recycling technologies can offer sustainable end-of-life options for plastic waste. While polyolefins can be converted into small hydrocarbons over acid catalysts at high temperatures, we demonstrate an alternative mechano-catalytic strategy at ambient conditions. The mechanism is fundamentally different from classical acidity-driven high-temperature approaches, exploiting mechanochemically generated radical intermediates. Surface activation of zirconia grinding spheres creates redox active surface sites directly at the point of mechanical energy input. This allows control over mechano-radical reactivity, while powder catalysts are not active. Optimized milling parameters enable the formation of 45% C1-10 hydrocarbons from polypropylene within 1 h at ambient temperature. While mechanochemical bond scission is undesired in plastic production, we show that it can also be exploited for chemical recycling.

Aliphatic Ketone Claisen Rearrangement: Troubleshooting the Transetherification Step by Identifying a Stable Acid Catalyst.

After optimization for retention of catalytic activity, 4-chlorobenzoic acid emerged as the optimal catalyst for the aliphatic ketone Claisen rearrangement. The optimal catalyst enables a one-pot, metal-free, catalytic protocol from allylic alcohols to γ,δ-unsaturated ketones. The optimized process tolerates a range of substrates, including substituents with acid-labile protecting groups. Reaction monitoring and DFT studies of the aliphatic ketone Claisen process agree that the ultimate rearrangement step typically has the highest activation barrier.

Post-Synthetic Modification of a 1D Mixed-Linker Zn(II) Coordination Polymer for Acid-Catalyzed Alcoholysis of Epoxides.

Rational design of heterogeneous acid catalysts possessing uniform dispersion of active sites plays a significant role in the catalytic performance. In the present work, a coordination polymer, [Zn(4,4´-bpy)(µ-Hbtc)(H2O)]∙2H2O (Zn-CP), was solvothermally synthesized using 4,4´-bpy (= 4,4´-bipyridine) and H3btc (= 1,3,5-benzenetricarboxylic acid) mixed linkers. Single crystal X-ray analysis of the polymer displayed that Zn-CP chains were decorated with 4,4´-bpy having unidentate coordination fashion. Then, the free N atom of the linker in Zn-CP was functionalized by -SO3H groups to afford Zn-CP-SO3H with enhanced acidity. The structures were characterized by FT-IR, thermogravimetric analysis, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of NH3 (NH3-TPD), and field emission scanning electron microscopy (FE-SEM) analyses. The coordination polymer was employed as heterogeneous catalyst for alcoholysis of epoxides under room conditions. The Zn-CP-SO3H exhibited excellent catalytic activity and regioselectivity in the methanolysis of styrene oxide within short reaction time.

Selective biomass conversion over novel designed tandem catalyst

Selective conversion of biomass into targeted molecules like polyols, especially, from cellulosic compounds, is being widely investigated as a sustainable process to produce biodiesel and bio-additives. The known process involves two steps, namely hydrolysis and hydrogenation. Thus, it requires two different catalytic materials or bifunctional catalysts. In this context, the present work reports a new catalytic approach based on the use of tandem catalysts, consisting of the combination of an acid solid catalyst (active for hydrolysis) and a supported metal catalyst (active for hydrogenation). Two different functionalized activated carbons and the resin Amberlyst 15 have been tested as solid acid catalysts, and Ru nanoparticles supported on the original activated carbon (SA) are the metal catalyst part of the tandem. All the tested tandem catalysts exhibited higher activity than the supported Ru catalyst did. The highest cellulose conversion and selectivity to sorbitol (70 % and 86 %, respectively) have been obtained over a novel tandem catalyst, which resulted from a physical mixture between a sulfuric acid modified SA carbon (SASu) and Ru loaded SA (Ru/SA), leading to a tandem catalyst (Ru/SA+SASu). This novel-designed tandem catalyst is reusable. Based on tandem catalysts with a solid-solid system combination, the adopted novel-designed catalytic approach is cost-efficient and sustainable, and can be considered promising for the green production of high-added-value chemicals.

UiO-66 with Both Brønsted and Lewis Acid Sites for Catalytic Synthesis of Biodiesel.

In the present study, an acid catalyst (UiO-66-SO3H) with Brønsted and Lewis acid sites was synthesised for the preparation of highly efficient biodiesel from oleic acid and methanol using chlorosulphonic acid sulfonated metal-organic frameworks (UiO-66) prepared with acetic acid as a moderator. The prepared catalysts were characterised using XRD, SEM, FT-IR and BET. The catalytic efficiency of the sulfonated catalysts was significantly improved and successful sulfonation was demonstrated by characterisation techniques. Biodiesel was synthesised by the one-pot method and an 85.0% biodiesel yield was achieved under optimum conditions of the reaction. The esterification reaction was determined to be consistent with a proposed primary reaction and the kinetics of the reaction was investigated. A reusability study of the catalyst (UiO-66-SO3H) was also carried out with good reproducibility. In conclusion, the present study provides some ideas for the synthesis of catalysts with high catalytic activity for the application in the catalytic preparation of biodiesel.

Catalytic Advantages of SO3H-Modified UiO-66(Zr) Materials Obtained via Microwave Synthesis in Friedel-Crafts Acylation Reaction.

The catalytic activity and stability of sulfonic-based UiO-66(Zr) materials were tested in the Friedel-Crafts acylation of anisole with acetic anhydride. The materials were prepared using microwave-assisted synthesis, producing microporous materials with remarkable crystallinity and physicochemical features as acid catalysts. Different ratios between both organic ligands, terephthalic acid (H2BDC) and monosodium 2-sulfoterephthalic acid (H2BDC-SO3Na), were used for the synthesis to modulate the sulfonic content. The sulfonic-based UiO-66(Zr) material synthesized with a H2BDC/H2BDC-SO3Na molar ratio of 40/60 exhibited the best catalytic performance in the acidic-catalyzed Friedel-Crafts acylation reaction. This ratio balanced the number of sulfonic acid sites and their accessibility within the UiO-66 microporous structure. The catalytic performance of this material increased remarkably at 200 °C, outperforming reference acids and commercial heterogeneous catalysts such as Nafion-SAC-13 and Amberlyst-70. Additionally, the best sulfonic-based UiO-66(Zr) material proved to be stable in four successive reaction cycles, maintaining both its catalytic activity and its structural integrity.

Lewis Acidic VOx Engineered PdAu Nanocatalysts for Efficient Formic Acid Dehydrogenation

AbstractThe development of high‐performance catalysts for formic acid (FA) dehydrogenation is of extreme significance to the successful production of hydrogen under ambient conditions. Despite some encouraging progress, their activity is still unsatisfied than needed. In this work, it is presented that Lewis acidic VOx sites engineered ultrafine PdAu nanoclusters (PdAu‐VOx) perform perfectly for hydrogen production from FA dehydrogenation. Strikingly, the best catalyst — PdAu‐VOx embed in amino‐functionalized hollow mesoporous support (PdAu‐VOx/NHMS) discloses an impressive initial turnover frequency of 14155 h−1 and a low activation energy of 31.2 kJ mol−1 without additives at room temperature, and maintains 100% selectivity and conversion in the tenth cycle reaction. Mechanistic investigations illustrate that VOx species can serve as the Lewis acid sites, which not only regulate the adsorption strength of reactant and intermediate on PdAu, but also reinforce the C─H bond activation within FA molecule, thereby promoting the reaction kinetics for efficient hydrogen production. This work thus provides a strategy for the development of new‐style heterogeneous catalysts with Lewis acid‐base sites applied to a variety of energy‐related catalytic reactions.

Enhancing Fenton-like reaction mediating performance of covalent organic frameworks through porosity modification

Covalent organic framework (COF) catalytic photocatalysts mediating Fenton-like reactions have been applied to the treatment of organic dyes in printing and dyeing wastewater. However, the photocatalytic performance of original COF is often unsatisfactory. This study investigated the impact of porosity modification strategies on the performance of COF photocatalysts in mediating the removal of organic dyes via Fenton-like reaction. Porosity modification was achieved by increasing the concentration of acetic acid (HAc) catalyst during COF preparation. The modified TAPB-DMTA COF (12M COF) exhibited excellent adsorption and photocatalytic properties. The Fenton-like reaction mediated by 12M COF photocatalysis removed nearly 96% of malachite green (MG) within 20 min, with a rate constant of 0.091 min−1, which was 2.9 and 6.5 times higher than that of g-C3N4 and original COF under the same reaction conditions, respectively. Additionally, the modulation mechanism of porosity modification on COF photocatalysis was explored. The conduction band (CB) of COF was reduced from −0.14 eV to −0.38 eV after porosity modification, facilitating the generation of longer-lived O2•- in the reaction system, which was conducive to efficient MG removal. Anti-interference experiments showed that the photocatalytic Fenton-like reaction system based on 12 M COF was less affected by common anions, cations and dissolved organics, while maintaining a high MG removal rate in tap water, mid-water, secondary clarifier effluent and river water. In summary, porosity modification was an effective strategy to improve the catalytic performance of original COFs. This study presented an efficient metal-free photocatalyst modification strategy for the Fenton-like reaction while avoiding the production of toxic by-products during dye degradation.

Direct application of tungstosilicic acid hydrate for the treatment of high free fatty acid in acidic crude palm oil and for biodiesel production

AbstractThis study explored the use of industrial acidic crude palm oil (ACPO) for biodiesel production, facing a significant obstacle due to its high free fatty acid (FFA) content, which complicates the biodiesel production process. Typically, esterification is employed to convert FFAs into fatty acid methyl ester (FAME). Herein, the effectiveness of tungstosilicic acid hydrate (TSAH) as an unsupported heteropoly acid (HPA) catalyst for FFA esterification in ACPO was investigated. The FFA content was reduced from 8.43% to 0.95% under optimum conditions (4 wt% catalyst dosage, a methanol to oil molar ratio of 10:1, 150 min and a temperature of 60°C). Noteworthy, the TSAH catalyst showed stability over 7 cycles. The kinetic analysis revealed that the FFA esterification process closely followed pseudo first‐order kinetics, with an R2 value of 0.94. Furthermore, the biodiesel produced from TSAH‐treated ACPO meets the standard specifications outlined by ASTM D6751 and EN 14214. This research highlights the effectiveness of TSAH in catalyzing FFA esterification without the need for additional support materials or modifications.

High-performance COFs composite nanofiltration membrane fabricated by organobase catalyst

Covalent Organic Frameworks (COFs) composite nanofiltration (NF) membrane has high permeation flux and rejection. However, the reaction rate of COFs is relatively slow. Adding acid catalyst is a common method to shorten reaction time. However, the dissatisfactory synthesis rate will lead to irregular structure of COFs materials. In this work, it is the first time to use organobase as a catalyst to prepare COFs composite membrane. The COFs structure will be optimized and the membrane performance can be enhanced. The prepared TpPa-PIP membrane compared with acid catalyzed TpPa-HAc membrane has better permeability, permeance of 89 L m−2·h−1·bar−1 and CR rejection of 99.54 %. This improvement is because of the TpPa-PIP intermediate made slower reaction speed that improves the overall regularity and crystallinity of COFs. Therefore, it is better method for broadening the application of organobase-catalyzed in preparing membranes.

Polyelectrolyte Additive-Modulated Interfacial Microenvironment Boosting CO2 Electrolysis in Acid.

Acidic CO2 electrolysis offers a promising strategy to achieve high carbon utilization and high energy efficiency. However, challenges remain in suppressing the competitive hydrogen evolution reaction (HER) and improving product selectivity. High concentrations of potassium ions (K+) can suppress HER and accelerate CO2 reduction, but they still inevitably suffer from salt precipitation problems. In this study, we demonstrate that the sulfonate-based polyelectrolyte, polystyrene sulfonate (PSS), enables to reconstruct the electrode-electrolyte interface to significantly enhance the acidic CO2 electrolysis. Mechanistic studies reveal that PSS induces high local K+ concentrations through electrostatic interaction between PSS anions and K+. In situ spectroscopy reveals that PSS reshapes the interfacial hydrogen-bond (H-bond) network, which is attributed to the H-bonds between PSS anions and hydrated proton as well as the steric hindrance of the additive molecules. This greatly weakens proton transfer kinetics and leads to the suppression of undesirable HER. As a result, a Faradaic efficiency of 93.9% for CO can be achieved at 250 mA cm-2, simultaneous with a high single-pass carbon efficiency of 72.2% on commercial Ag catalysts in acid. This study highlights the important role of the electrode-electrolyte interface induced by polyelectrolyte additives in promoting electrocatalytic reactions.

Polyelectrolyte Additive‐Modulated Interfacial Microenvironment Boosting CO2 Electrolysis in Acid

Acidic CO2 electrolysis offers a promising strategy to achieve high carbon utilization and high energy efficiency. However, challenges remain in suppressing the competitive hydrogen evolution reaction (HER) and improving product selectivity. High concentrations of potassium ions (K+) can suppress HER and accelerate CO2 reduction, but they still inevitably suffer from salt precipitation problems. In this study, we demonstrate that the sulfonate‐based polyelectrolyte, polystyrene sulfonate (PSS), enables to reconstruct the electrode‐electrolyte interface to significantly enhance the acidic CO2 electrolysis. Mechanistic studies reveal that PSS induces high local K+ concentrations through electrostatic interaction between PSS anions and K+. In situ spectroscopy reveals that PSS reshapes the interfacial hydrogen–bond (H–bond) network, which is attributed to the H–bonds between PSS anions and hydrated proton as well as the steric hindrance of the additive molecules. This greatly weakens proton transfer kinetics and leads to the suppression of undesirable HER. As a result, a Faradaic efficiency of 93.9% for CO can be achieved at 250 mA cm–2, simultaneous with a high single‐pass carbon efficiency of 72.2% on commercial Ag catalysts in acid. This study highlights the important role of the electrode‐electrolyte interface induced by polyelectrolyte additives in promoting electrocatalytic reactions.