Solid Acid Base Catalysts Research Articles

Solid Acid–Base Catalysts Based on Layered Double Hydroxides Applied for Green Catalytic Transformations

Layered double hydroxides (LDHs) have emerged as promising catalysts for various acid–base catalytic reactions. Due to their unique structure and regulatable dual acid–base properties, they offer more environmentally friendly and sustainable alternatives to traditional liquid acid and base catalysts. This study introduces the structural composition, preparation methods, and acid–base catalytic properties of LDH-based catalysts. Recent application progress in LDHs and rehydrated LDHs, LDH-based metal nanocatalysts, and LDH-based mixed metal oxide catalysts used as solid acid–base catalysts in acid–base green catalytic conversion is reviewed. The challenges and prospects of LDH-based catalysts as green and sustainable catalysts are summarized and proposed.

New Usage of Molecular Sieves

Molecular sieves are type A zeolites with specific sized pores and are commonly used in organic synthesis to capture small molecules such as water. In addition to their trapping effect, they also have acidic and basic active sites and are used as solid acid-base catalysts. Usually, heat-drying treatments are performed prior to use, but the heat treatment methods, such as microwave ovens or heat guns, are not standardized, which could cause problems in reproducibility of reactions. Particularly, for reactions requiring acid/base sites of molecular sieves, these treatment methods are considered more sensitive because the structure of the active sites changes upon heating. In this article, we propose new methods of activation when using molecular sieves and their application to continuous-flow reactions.

Investigation of the Acid/Basic Sites of Zeolite Trough Some Catalysed Nucleophilic Reactions

Zeolites, both natural and synthetic, are certainly some of the most versatile minerals for their applications. Since the 1940s, they have been used in the chemical industry as catalysts, adsorbents and ion exchanger extensively, and the development of their practical usage is expected to continue upon years. Their versatility is the result of the combination of peculiar and indispensable properties, each of which can be found in other material as a single property, but seldom all of them are found in combination. However, despite the success of their employment, the mechanisms of many important catalytic processes involving zeolites remained elusive. In particular, the comprehension of the structure–property relationships for emerging applications are highly required. In this perspective article we focus on the role of zeolites as solid acid-base catalysts. We go deeply into the structural properties of the LTA kind (Zeolite-Na A 4 Ångstrom) that was successfully employed as basic catalyst for several nucleophilic substitution reactions.

Sustainable production of styrene from catalytic recycling of polystyrene over potassium promoted Fe–Al2O3 catalyst

The catalytic degradation of polystyrene into styrene was comprehensively studied over solid acid–base catalysts.

Catalytic dehydration of glucose to 5-HMF using heterogeneous solid catalysts in a biphasic continuous-flow tubular reactor

This work aimed to produce 5-hydroxymethylfurfural (5-HMF) from glucose in a biphasic continuous-flow tubular reactor with various heterogeneous solid acid catalysts or combined solid acid-base catalysts. Among the catalysts tested, niobium phosphate (NbP) was found to be the most active catalyst for glucose dehydration with a maximum 5-HMF yield of 45% at 150 °C. The higher activity of NbP was attributed to its higher total number of acid sites and BET surface area, as well as the presence of both Lewis acid and Brønsted acid sites. The effects of different operating conditions such as aqueous to organic (A/O) phase ratio, reaction temperature and feeding flow rate on the activity of some selected catalysts were studied. Reducing A/O ratio by increasing the extracting organic phase flow rate and increasing the reaction temperature (up to 150 °C) were found to positively affect 5-HMF production from glucose in the presence of NbP. Kinetics study demonstrated that the overall reaction of glucose dehydration to 5-HMF over the NbP catalyst is a first-order reaction with the reaction rate constants (k) determined as 0.06, 0.21 and 0.6 min−1 at 110, 130 and 150 °C, respectively, and the apparent activation energy (Ea) calculated to be 77 kJ/mol.

Evaluating Energy-Efficient Solutions of CO2 Capture within Tri-solvent MEA+BEA+AMP within 0.1+2+2–0.5+2+2 mol/L Combining Heterogeneous Acid–Base Catalysts

To reduce the extensive energy penalty of CO₂ desorption process of amine-based CO₂ capture technology, the combination of “coordinative effect” with “heterogeneous catalysis” was adopted into “MEA+BEA+AMP” tri-solvents at special concentrations (0.1–0.5+2+2 mol/L) with solid base catalysts “CaCO₃” and various solid acid catalysts “γ-Al₂O₃, H-ZSM-5, and blended γ-Al₂O₃/H-ZSM-5”. Experiments were performed to evaluate if there were synergetic effects within the optimization of amine blend concentrations and catalyst selections. Reaction schemes were investigated within the tri-solvents to understand the absorption and desorption mechanisms of coordinative effect. CO₂ absorption was performed at 40 °C, and CO₂ desorption was performed at 90 °C. Five tri-solvent compositions with various catalysts were investigated in terms of initial absorption rate (Iₐbₛ), initial desorption rate (Idₑₛ), heat duty (H), and cyclic capacities, which were categorized into absorption–desorption parameters systematically. The results indicated that tri-solvents with catalysts were highly energy-efficient. The optimized tri-blend was 0.3+2+2 mol/L MEA+BEA+AMP, which performed better than the 2+2 mol/L BEA+AMP benchmark on both absorption and desorption. The optimized regeneration performance of tri-blends was 0.3+2+2 mol/L, and its relative heat duty was 32.9% of that of 5 M MEA and 66.5% of that of 2+2 M BEA+AMP. Results manifested that the combination of solid acid–base catalysts with tri-solvents containing “coordinative effects” was a promising solution to further optimize the energy efficiency of CO₂ absorption–desorption within industrial amine-based CO₂ capture processes.

Alkali Potassium Induced HCl/CO2 Selectivity Enhancement and Chlorination Reaction Inhibition for Catalytic Oxidation of Chloroaromatics

Industrial combustion of chloroaromatics is likely to generate unintentional biphenyls (PCBs), polychlorinated dibenzo- p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). This process involves a surface-mediated reaction and can be accelerated in the presence of a catalyst. In the past decade, the effect of surface nature of applied catalysts on the conversion of chloroaromatics to PCBs/PCDD/PCDF has been well explored. However, studies on how the flue gas interferent components affect such a conversion process remain insufficient. In this article, a critical flue gas interferent component, alkali potassium, was investigated to reveal its effect on the chloroaromatics oxidation at a typical solid acid-base catalyst, Mn xCe1- xO2/HZSM-5. The loading of alkali potassium was found to improve the Lewis acidity of the catalyst (by increasing the amounts of surface Mn4+ after calcination), which thus promoted the CO2 selectivity for catalytic chlorobenzene (CB) oxidation. The KOH with a high hydrophilicity has favored the adsorption/activation of H2O molecules that provided sufficient hydroxyl groups and possibly induced a hydrolysis process to promote the formation of HCl. The K ion also served as a potential sink for chorine ions immobilization (via forming KCl). Both of these inhibited the formation of phenyl polychloride byproducts, thereby blocking the conversion of CB to chlorophenol and then PCDDs/PCDFs, and potentially ensuring a durable operation and less secondary pollution for the catalytic chloroaromatics combustion in industry.

Selective transformation of glucose into propylene glycol on Ru/C catalysts combined with ZnO under low hydrogen pressures

Recently, biomass resources have garnered significant attention as sustainable and renewable raw materials for the production of chemicals. Propylene glycol (PG) is a valuable chemical product that can be synthesized from biomass. Herein, the selective transformation of glucose into PG was investigated on a carbon-supported 5wt% Ru catalyst (5%-Ru/C) combined with solid acid–base catalysts under low hydrogen pressures. The reaction conditions, namely the amount of ZnO, temperature, and hydrogen pressure, were also evaluated. At a hydrogen pressure of 0.4MPa, a full conversion of glucose and 38% yield of PG were obtained using the ZnO+Ru/C system at 453K for 20h, while the yield of PG on Ru/C alone was only 9.3% under the same conditions. Studies on the reaction mechanism indicated that the transformation of glucose into PG consisted of the isomerization of glucose to fructose, retro-aldol reaction of fructose to triose (dihydroxyacetone and glyceraldehyde), dehydration of glyceraldehyde to pyruvaldehyde, and successive hydrogenation of pyruvaldehyde to PG via hydroxyacetone. The ZnO catalyst promoted both the isomerization and retro-aldol reaction steps, and the Ru catalyst promoted the hydrogenation steps. The retro-aldol reaction, which included the cleavage of C3C4 bond in glucose, enabled the selective transformation of glucose into PG under low hydrogen pressures. These findings provide novel insights into the efficient synthesis of PG from glucose, which could be achieved by combining and optimizing the retro-aldol and hydrogenation steps.

Synthesis and application of novel solid acid-base catalysts for side chain alkylation of toluene with methanol

Novel solid acid-base catalysts with aluminum and nitrogen were prepared from phenolic compounds and formaldehyde by using triblock copolymer Pluronic F127 as a template via evaporation induced organic-organic assembly method. The catalysts were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The acid-base properties of the catalyst were determined by temperature programmed desorption (TPD) using CO2 and NH3 as probe molecules. The side chain alkylation of toluene with methanol over the catalyst was studied, the results demonstrated that the catalyst Cat-TDMMP was of the higher activity [(ethylbenzene + styrene) yield was 41.0%] than the conventional alkali exchanged zeolites [(ethylbenzene + styrene) yield was about 20%]. This fact may due to the strength and distance of the specific surface acid-base pairs of the catalyst, which are favored to bimolecular side-chain alkylation reaction.

X-ray Absorption Spectroscopic Characterization of Solid Acid-base Catalysts

Recent X-ray absorption spectroscopic studies of solid acid-base catalysts were reviewed, which have been carried out to investigate the effects of lanthanum-ion addition to alumina for improving the thermal stability, acidity generation mechanism of siliceous mesoporous silica, or state of tungsten oxide species in WOx–ZrO2 strong solid acid. Remarks on EXAFS analytical procedures were also discussed about possibility of coexistence of multiple phases, mismatch between radial distribution functions and Fourier transforms of EXAFS, and effects of multiple excitations in an X-ray absorption spectrum.

Synthesis of novel polymer as solid acid-base catalyst for styrene from toluene

A novel solid acid-base catalyst Cat-NH2C2H4NH2 with aluminum and nitrogen was prepared from phenol and formaldehyde by using triblock copolymer Pluronic F127 as a template and resol as a catalyst precursor via evaporation induced organic-organic assembly method. The catalyst was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The acid-base properties of the catalyst were determined by temperature programmed desorption (TPD) using CO2 and NH3 as probe molecules. The side chain alkylation of toluene with methanol over the catalysts had been studied. The results showed that Cat-NH2C2H4NH2 has demonstrated the higher activity and selectivity than the conventional alkali exchanged zeolites. This may be because that the weak or middle acid-base pairs on the catalyst are favored to bimolecular side-chain alkylation reaction.

Comparison of gas-phase dehydration of propane polyols over solid acid–base catalysts

Gas-phase dehydration of aqueous propane polyols including glycerol, 1,2- and 1,3-propanediols was investigated over various solid catalysts with a wide range of acid–base properties. Fairly high selectivity (40–75mol%) for propanal formation from 1,2-propanediol, and acrolein from glycerol was obtained over the catalysts with high fractional acidity in the range of −8.2<H0≤−3.0, in which Brønsted acidity appeared advantageous over Lewis acidity. The dehydration of 1,3-propanediol produced quite scattered products and a clear relationship between its product selectivity and the catalyst acidity could not be established. Mechanistic implications of these observations are discussed, which point to that the dehydration reactions of both 1,2-propanediol and glycerol are initiated by activation of the hydroxyl group bonded with the central carbon atoms.

The Dehydration of Methanol to Dimethyl Ether over a Novel Solid Acid-base Catalyst

A novel polymer solid acid-base catalyst Cat-AAA (Al + aminoacetic acid) with aluminum and nitrogen was prepared from aminoacetic acid and Al by using triblock copolymer Pluronic F127 as a template via evaporation induced organic–organic assembly method. Cat-AAA was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectra. The acid-base properties of the catalysts were determined by temperature programmed desorption using CO2 and NH3 as probe molecules. The dehydration of methanol to dimethyl ether over Cat-AAA had been studied; the results showed that the conversion of methanol and selectivity of dimethyl ether is higher at a high reaction temperature. The key requirements for a good catalyst for dehydration of methanol to dimethyl ether are: (i) weak acid-sites activate O in a methanol molecule; (ii) at the same time, weak base-sites activate H of hydroxy group in another methanol molecule.

Amine functionalized K10 montmorillonite: a solid acid–base catalyst for the Knoevenagel condensation reaction

Different amine functionalized K10 montmorillonites were hydrothermally fabricated by a simple method of treatment of the neat clay with different amine solutions and used as heterogeneous catalysts towards the Knoevenagel condensation reaction. Catalytic results show that the di-amine functionalized K10 montmorillonite exhibits high efficacy for promoting this reaction at room temperature and in the absence of a solvent. The solid catalyst was characterized using a variety of different techniques; including Fourier transform infrared spectroscopy (FT-IR), nitrogen physisorption measurements, (29)Si CP MAS NMR spectroscopy, NH3-temperature programmed desorption (NH3-TPD), X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FESEM). The catalyst could be recycled and reused for several runs without any loss of inherent catalytic activity.

Styrene from Toluene by Side Chain Alkylation over a Novel Solid Acid-base Catalyst

A novel solid acid-base catalyst with aluminum and nitrogen was prepared from aluminum and amine by using triblock copolymer Pluronic F127 as a template and resol as a framework via evaporation-induced organic–organic assembly method. The catalyst was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectra. The acid-base properties of the catalyst were determined by temperature-programmed desorption using CO2 and NH3 as probe molecules, and the side chain alkylation of toluene with methanol over the catalyst has been investigated. The results show that the catalyst demonstrates the higher activity and selectivity.

Side-chain Alkylation of Toluene With Methanol over a Novel Solid Acid-base Catalyst

A novel solid acid-base catalyst Cat-NH(CH3)2 with aluminum and nitrogen was prepared from phenol and formaldehyde by using the triblock copolymer Pluronic F127 as a template and resol as a catalyst precursor via evaporation induced by the organic–organic assembly method. The catalyst was characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The base properties of the catalyst were determined by temperature programmed desorption using CO2 as a probe molecule. The side chain alkylation of toluene with methanol over the catalyst had been studied, the results showed that Cat-NH(CH3)2 has demonstrated a higher activity and selectivity than the alkali exchanged zeolites. This may be because the strength of the specific surface base sites of this catalyst is favored to bimolecular side-chain alkylation reaction.

Styrene from toluene by side chain alkylation over a novel solid acid-base catalyst

A novel solid acid-base catalyst with aluminum and nitrogen were prepared from aluminum and amine by using triblock copolymer Pluronic F127 as a template and resol as framework via evaporation induced organic–organic assembly method. The catalyst was characterized by UV–vis absorption spectra (UV–vis), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), the acid-base properties of the catalyst were determined by temperature programmed desorption (TPD) using CO 2 and NH 3 as probe molecules, and the side chain alkylation of toluene with methanol over the catalyst has been investigated. The results show that Cat–NH(C 2H 5) 2 demonstrates the higher activity and selectivity, styrene yield reaches 44.9% and selectivity 97.6%. It is considered that the strength of base and distance of the specific surface acid-base pairs over the catalysts are favored to bimolecular side-chain alkylation reaction.

ChemInform Abstract: Appraisal of Heterogeneous Solid Acid—Base Catalysts for Transesterification

AbstractReview: 74 refs.

Monoglyceride synthesis by glycerolysis of methyl oleate on solid acid–base catalysts

The synthesis of monoglycerides by glycerolysis of methyl oleate, an unsaturated fatty acid methyl ester, was studied on acid–base solid catalysts as an alternative to the current commercial technology that uses liquid base catalysts. Initially, the reaction conditions such as catalyst particle size and stirring rate required for operating the four-phase semi-continuous reactor under a kinetically controlled-regime were determined. Then the optimization of the reaction parameters for achieving high monoglyceride yields was performed using MgO. MgO compared favorably with the corresponding homogeneously catalyzed process. In fact, when using high reaction temperatures (493–523 K), glycerol/methyl oleate molar ratios between 2 and 6, and catalyst/reactant ratios of about 30 g/mol, glycerolysis of methyl oleate yields up to 77% monoglycerides in 2 h, a much higher value than those usually obtained via the liquid base-catalyzed homogeneous process (40–60%). The acid–base site requirements for the glycerolysis reaction were investigated using single oxides with different electronegativities. A good correlation was found between the catalytic activity and the base site density. In addition, results show that glycerolysis of methyl oleate requires strong base sites such as those of MgO.

Sustainable production of acrolein: investigation of solid acid–base catalysts for gas-phase dehydration of glycerol

Synthesis of acrolein by catalytic gas-phase dehydration of biomass-derivate glycerol was studied over various solid catalysts with a wide range of acid–base properties. The catalyst acidity and basicity were measured, respectively, by n-butylamine and benzoic acid titration methods using Hammett indicators. The most effective acid strength for the selective dehydration of glycerol to form acrolein appeared between −8.2 ≤ H0 ≤ −3.0, with which acrolein was produced at a selectivity of 60–70 mol%. The catalysts having very strong acid sites (H0 ≤ −8.2) effected a lower acrolein selectivity (40–50 mol%) due to more severe coke deposition in the reaction. Solid acids holding medium strong and weak acid sites (−3.0 ≤ H0 ≤ +6.8) were found to be not selective for the acrolein production, the acrolein selectivity being less than 30 mol%. The mass specific catalytic rate for the acrolein production showed a general trend to increase with the fractional acidity at −8.2 ≤ H0 ≤ −3.0. The catalytic data also suggest that Bronsted acid sites were advantageous over Lewis acid sites in catalyzing the selective synthesis of acrolein from glycerol dehydration. Solid base catalysts were shown not to be effective for acrolein production.