Acid Base Bifunctional Catalysts Research Articles

Overcoming acid–base copolymer neutralization using mesoporous carbon and its catalytic activity in the tandem deacetalization–Knoevenagel condensation reaction

Acid–base copolymer materials are of considerable interest because of their fundamental implications for acid–base bifunctional catalysis applications. However, quenching the acid and base sites of the copolymer with each other in free radical polymerizations is still challenging. Herein, we demonstrate that the polymerization of styrenesulfonic acid-co-4-vinylpyridine into the mesoporous carbon material (i.e., CMK-3) can control the chain growth polymerization and result in decreasing the interaction of the acid–base sites. The results showed that by using CMK-3, 40% of the acid and base sites of the copolymer remain in their original form while 60% of acid and base sites convert to the pyridinium and sulfonate forms. Furthermore, it is demonstrated that this material can be processed as a heterogeneous bifunctional acid–base catalyst in the tandem one-pot acid–base reaction (i.e., deacetalization–Knoevenagel condensation reaction) with a high catalytic activity in aqueous media.

Mg–Al Mixed Oxide Derived from Hydrotalcites Prepared Using the Solvent-Free Method: A Stable Acid–Base Bifunctional Catalyst for Continuous-Flow Transesterification of Dimethyl Carbonate and Ethanol

Mg–Al oxides were prepared by facile solvent-free grinding of Mg–Al layered double hydroxide and were used as catalysts for continuous-flow transesterification of dimethyl carbonate and ethanol. Th...

One-pot synthesis of HMF from carbohydrates over acid-base bi-functional carbonaceous catalyst supported on halloysite nanotubes

Nitrogen-doped carbon materials have attracted enormous interest in catalysis owing to their outstanding catalytic performance. In this work, nitrogen-doped carbonaceous catalysts (NCC) supported on inexpensive and naturally abundant halloysite nanotubes were successfully synthesized via precipitation polymerization, calcination, and sulfonation processes. The physical and chemical properties of the obtained catalysts were systematically characterized by different methods. The results indicated that NCC catalysts had mesoporous structures, excellent thermostability and acid-base bi-functional active sites. One-pot synthesis of 5-hydroxymethylfurfural (HMF) from glucose was performed to investigate the synthesized NCC catalysts. Benefiting from the synergistic effects of the acid-base bi-functional active sites, the highest HMF yield (62.8%) was achieved in an isopropanol-mediated DMSO system under optimal conditions. Moderate to excellent yields of HMF were also obtained from one-pot conversions of other carbohydrates, including inulin, sucrose, cellobiose, maltose and starch, with our developed catalytic system. The one-pot production of HMF from cellulose was also smoothly processed by the NCC bi-functional catalyst in an IL-based system. This work has developed a versatile strategy for designing nitrogen-doped carbonaceous catalysts that can be employed for the direct transformation of renewable carbohydrates to platform chemicals.

Functionalized cellulose nanofibril aerogels as cooperative acid–base organocatalysts for liquid flow reactions

Cellulose nanomaterial aerogels are macroscopic porous solids with relatively high surface areas and are thus an interesting basis for renewable catalyst materials. Cross-linked acid–base bifunctional catalyst aerogels are produced here from TEMPO-oxidized cellulose nanofibrils (TOCNF) and demonstrated in both batch and flow catalysis. Recently established acid–base modification for catalysis is expanded upon for chemical or physical cross-linking with small molecules and polymers. Low density and relatively high surface area (up to 74 m2 g−1) aerogel catalysts are produced with a variety of processing approaches and then freeze-dried from water or tert-butyl alcohol/water mixtures. Finer pore structure and increased surface area are achieved with tert-butyl alcohol as co-solvent. Chemical cross-linking improved aerogel stability to solvents. Homogeneous and aerogel TOCNF catalysts are shown to be effective acid–base cooperative catalysts for aldol condensation reactions in batch reactions. Continuous flow reactions are performed with glass column reactors packed with aerogel catalysts that showed improved rates relative to batch experiments, while also demonstrating physical stability. Catalyst deactivation in flow reactions is observed and observations of deactivation support previously reported mechanisms of site poisoning by competitive chemisorption of reactants in analogous acid–base catalysts. This report is a key demonstration of cellulose nanofibril aerogels for catalysis in continuous liquid flow reactions.

Development of bimetallic nickel-based catalysts supported on activated carbon for green fuel production

In this work, the catalytic deoxygenation of waste cooking oil (WCO) over acid–base bifunctional catalysts (NiLa, NiCe, NiFe, NiMn, NiZn, and NiW) supported on activated carbon (AC) was investigated. A high hydrocarbon yield above 60% with lower oxygenated species was found in the liquid product, with the product being selective toward n-(C15 + C17)-diesel fractions. The predominance of n-(C15 + C17) hydrocarbons with the concurrent production of CO and CO2, indicated that the deoxygenation pathway proceeded via decarbonylation and decarboxylation mechanisms. High deoxygenation activity with better n-(C15 + C17) selectivity over NiLa/AC exposed the great synergistic interaction between La and Ni, and the compatibility of the acid–base sites increased the removal of oxygenated species. The effect of La on the deoxygenation reaction performance was investigated and it was found that a high percentage of La species would be beneficial for the removal of C–O bonded species. The optimum deoxygenation activity of 88% hydrocarbon yield with 75% n-(C15 + C17) selectivity was obtained over 20% of La, which strongly evinced that La leads to a greater enhancement of the deoxygenation activity. The NiLa/AC reusability study showed consistent deoxygenation reactions with 80% hydrocarbon yield and 60% n-(C15 + C17) hydrocarbon selectivity within 6 runs.

Immobilized piperazine on the surface of graphene oxide as a heterogeneous bifunctional acid–base catalyst for the multicomponent synthesis of 2-amino-3-cyano-4H-chromenes

A green method for the efficient synthesis of 2-amino-3-cyano-4H-chromenes using immobilized piperazine on the surface of graphene oxide (piperazine-GO) as a new heterogeneous bifunctional acid–base catalyst is developed.

One-pot synthesis of bimetallic metal–organic frameworks (MOFs) as acid–base bifunctional catalysts for tandem reaction

Bimetallic MIL-101(Al/Fe)–NH2 exhibits enhanced acid–base bifunctional catalytic activity due to its synergistic mechanism and hierarchical pore system.

Black yet green: Sulfonic acid functionalized carbon as an efficent catalyst for highly selective isomerization of α-pinene oxide to trans-carveol

In this study, an inexpensive, high yielding, and environmentally benign bifunctional acid-base catalyst is prepared using a simple low-temperature hydrothermal carbonization method from a fishery bio-waste, chitosan as a carbon source and sulfuric acid, as _SO3H source. The successful formation of _SO3H group grafted carbon was confirmed by various physiochemical characterization methods such as powder XRD, FTIR, RAMAN, FESEM, EDAX, HRTEM, and XPS. Under the optimized reaction conditions, the bio-derived sulfonated hydrothermal carbon catalyst showed excellent performance for the isomerization of α-pinene oxide to trans-carveol (85% yield) at 160 °C in 1.5 h. The product selectivity was influenced mainly by the type of solvent used for the isomerization. No leaching of the sulfonated groups was observed even after five cycles without any significant loss in conversion and selectivity.

Facile Synthesis of a Highly Effective Layered Double Hydroxide Catalyst and Its Application in the One-Step Ethoxylation of Butyl Acetate to Oligo-Ethylene Glycol Butyl Ether Acetates

A novel synthetic route for the one-step ethoxylation of butyl acetate to form oligo-ethylene glycol butyl ether acetates is explored by adopting an effective acid–base bifunctional catalyst in a fixed-bed reactor. The highly efficient hydrotalcite-type catalysts used are prepared by employing co-precipitation methods. After treatment with arachidic acid, the as-obtained catalyst gives higher butyl acetate conversion and better ethylene oxide catalytic activity with a narrower adduct distribution of ethylene glycol butyl ether acetate in a fixed-bed reactor. After the reaction for 72 h, the conversion of butyl acetate was over 10% and the selectivities for both 1-ethylene glycol butyl ether acetate and 2-ethylene glycol butyl ether acetate arrived at more than 40%.

Tunable Acid-Base Bifunction of Hierarchical Aluminum-Rich Zeolites for the One-Pot Tandem Deacetalization-Henry Reaction.

The development of bifunctional catalysts is important in the synthesis of materials for multiple sequential reactions in one-pot tandem catalytic processes. In this context, a dealuminated acid-base bifunctional catalyst with a hierarchical aluminum-rich faujasite structure (zeolite Y) has been successfully prepared by the solid-state dealumination of NaX nanosheets with ammonium hexafluorosilicate (AHFS). The characteristic properties of catalysts were examined by means of XRD, SEM, TEM, N2 physisorption technique, ICP-OES, NH3 -TPD, CO2 -TPD, 27 Al NMR, 29 Si NMR, Al K-edge XANES, and Pyridine-FTIR. The materials exhibit a superior catalytic performance for one-pot tandem catalysis, for example, the synthesis of trans-β-nitrostyrene with a yield close to 100 % in a tandem deacetalization-Henry reaction of benzaldehyde dimethyl acetal with nitromethane. The high catalytic performance is attributed to the facile transfer of bulky molecules between acid and basic sites in the presence of hierarchical structures.

Dual-functionalized ZIF-8 as an efficient acid-base bifunctional catalyst for the one-pot tandem reaction

An acid-base bifunctional zeolitic imidazolate framework catalyst (ZIF8-A61-SO3H) with amine and sulfonic acid groups was successfully prepared through simple two step post-synthetic modification: preparation of amine-functionalized ZIF-8 with amine contents of 61% (ZIF8-A61) by the ligand exchange of 2-mIM with 3-amino-1,2,4-triazole (Atz), followed by the sulfonic acid functionalization by the ring-opening reaction of 1,3-propanesultone with –NH2 groups in ZIF8-A61. Amine-functionalized ZIF8-A materials with difference amine contents (15%, 34%, and 61%, respectively) were also prepared by controlling the synthesis time. All obtained ZIF catalysts evaluated as a heterogeneous catalyst for one-pot deacetalization-Knoevenagel condensation tandem reaction. Compared with ZIF-8 and amine-functionalized ZIF-8 catalysts, ZIF8-A61-SO3H catalyst showed good catalytic performance with 100% conversion of the reactant and 98% selectivity of the final Knoevenagel product. An enhanced catalytic activity can be attributed to the co-existence of site-isolated acid-base groups on the ZIF8-A61-SO3H catalyst in close proximity. The heterogeneous nature of the catalytic system was confirmed by a hot-filtering test and the catalyst also exhibited reusable in the five repeated cycles. A plausible catalytic mechanism of deacetalization-Knoevenagel condensation reaction over ZIF8-A61-SO3H was also proposed.

Acid–base bifunctional magnesium oxide catalyst prepared from a simple hydrogen peroxide treatment for highly selective synthesis of jasminaldehyde

ABSTRACT The aldol reaction between benzaldehyde and heptanal for jasminaldehyde synthesis has been widely tested over various heterogeneous catalysts. The reaction is preferred to be conducted over acid-base bifunctional catalyst for high jasminaldehyde selectivity. Generally, Magnesium oxide (MgO) is not considered to be suitable for jasminaldehyde synthesis due to its monobasic property and low jasminaldehyde selectivity. In this work, the MgO sample was treated through a simple hydrogen peroxide reflux-calcination process to create acid-base bifunctional surface. The resulting catalyst afforded high selectivity to jasminaldehyde of 88–90% even at a benzaldehyde to heptanal molar ratio of 5. The mechanism of this high jasminaldehyde selectivity was investigated in this paper, and the results indicate that this novel acid-base bifunctional MgO catalyst is preferential adsorption of benzaldehyde over heptanal, which leads to a higher benzaldehyde: heptanal ratio on its surface. In addition, the presence of weak Lewis acid sites on catalyst’s surface induces a partial positive charge on carbonyl group of benzaldehyde, making it susceptible to a nucleophilic attack by the heptanal carbanion. The reusability of this novel acid-base bifunctional MgO catalyst was also studied.

Zn-Zr-Al oxides derived from hydrotalcite precursors for ethanol conversion to diethyl carbonate

Ethanol conversion to high-value-added products has attracted considerable attention in both academic research and industrial fields. In this study, we synthesized a series of tunable acid–base bifunctional Zn-Zr-Al metal oxides (represented as Zn2ZrxAl-MMO) in light of the structural topotactic transformation of Zn2ZrxAl-hydrotalcite precursors (Zn2ZrxAl-LDH). The resulting Zn2ZrxAl-MMO catalysts were employed in the conversion of ethanol to diethyl carbonate. The Zr4+ ion content of the LDH precursor plays a key role in modulating the acid-base properties and determining catalytic performance: the Zn2Zr0.1Al-MMO sample exhibits the optimal catalytic behavior with a diethyl carbonate (DEC) yield of 42.1%, which is the highest reported for metal oxide catalysts. Structure-property correlation investigations revealed that the synergic catalysis between medium-strong basic sites and weak acid sites plays a predominant role in the catalytic behavior. Furthermore, in situ Fourier transform infrared measurements showed that the weak acidic site promotes activation adsorption of the reactant (urea) and the intermediate product (ethyl carbamate), while the medium-strong basic site accelerates ethanol activation. Moreover, the Zn2Zr0.1Al-MMO catalyst has the advantages of cost effectiveness, good stability, and reusability. Therefore, the acid-base bifunctional catalysts developed in this work can be employed as promising candidates in acid-base catalytic reactions such as ethanol conversion.

MgO nanoparticles confined in ZIF-8 as acid-base bifunctional catalysts for enhanced glycerol carbonate production from transesterification of glycerol and dimethyl carbonate

Abstract MgO-loaded ZIF-8 catalysts (MgO@ZIF-8) with various MgO loadings were prepared and characterized using atomic absorption spectroscopy (AAS), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), N2 sorption isotherms, field-emission transmission electron microscopy (FE-TEM), and thermogravimetric analysis (TGA). Our results indicate that MgO nanoparticles could deposit onto the ZIF-8 surface with high atom efficiency while maintaining the ZIF-8 structure through a wet-impregnation and calcination process. It is suggested that the surface sites and microporosity of ZIF-8 support provide an adequate environment for the initial deposition of Mg precursor and subsequent growth of MgO nanoparticles through a nanoconfinement effect. MgO@ZIF-8 catalysts were tested for catalytic transesterification of glycerol and dimethyl carbonate to yield glycerol carbonate. It is found that the 50 wt% MgO@ZIF-8 catalyst display an improved catalytic activity than those of MgO and ZIF-8. Furthermore, the MgO@ZIF-8 catalysts showed higher catalytic activities than their physically-mixed counterparts, indicative of a synergistic effect between MgO and ZIF-8, which is explained by a proposed mechanism based on acid-base bifunctional sites on the surface.

Synthesis of multifunctional polymer containing Ni‐Pd NPs via thiol‐ene reaction for one‐pot cascade reactions

Recently, acid–base bifunctional catalysts have been considered due to their abilities, such as the simultaneous activation of electrophilic and nucleophilic species and their high importance in organic syntheses. However, the synthesis of acid–base catalysts is problematic due to the neutralization of acidic and basic groups. This work reports a facial approach to solve this problem via the synthesis of a novel bifunctional polymer using inexpensive materials and easy methods. In this way, at the first step, heterogeneous poly (styrene sulfonic acid‐n‐vinylimidazole) containing pentaerythritol tetra‐(3‐mercaptopropionate) (PETMP) and trimethylolpropane trimethacrylate (TMPTMA) cross‐linkers were synthesized in the pores of a mesoporous silica structure using click reaction as a novel bifunctional acid–base catalyst. After that, Ni‐Pd nanoparticles supported on poly (styrenesulfonic acid‐n‐vinylimidazole)/KIT‐6 as a novel trifunctional heterogeneous acid–base‐metal catalyst was prepared. The prepared catalysts were characterized by various techniques like FT‐IR, TGA, ICP‐AES, DRS‐UV, TEM, FE‐SEM, EDS‐Mapping, and XRD. The synthesized catalysts were efficiently used as bifunctional/trifunctional catalysts for one‐pot, deacetalization‐Knoevenagel condensation and one‐pot, three‐step and a sequential reaction containing deacetalization‐Knoevenagel condensation‐reduction reaction. It is important to note that the synthesized catalyst showing high chemo‐selectivity for the reduction of nitro group, alkenyl double bond and ester group in the presence of nitrile. Moreover, it was found that the different nanoparticles including Ni, Pd, and alloyed Ni‐Pd showing different chemo‐selectivity and catalytic activity in the reaction.

Synergistic catalysis of one-pot cascade reactions by acidic and basic binary porous polymers

Acidic and basic porous polymers were facilely prepared through the radical copolymerization of target monomers and the crosslinker divinylbenzene (DVB), respectively. Combination of these polymers endowed highly efficient, heterogeneous recyclable acid-base binary catalysts for cascade deacetalization-Knoevenagel reaction, offering high yield and stable reusability. Binary polymers with strong acid sites and superior base sites afforded an unprecedented turnover frequency (TOF) in the condensation of benzaldehyde dimethylacetal and nitriles (285 h−1 for malononitrile and 57 h−1 for inert methylene substrate ethyl cyanoacetate). The excellent synergistically catalytic performance was ascribed to the unique self-protection effect of the in-situ formed acid and base sites embedded in the polymeric network. This study provided a facile, versatile and efficient strategy towards acid-base bifunctional heterogeneous catalysts by combining acidic and basic porous polymers.

Efficient Catalytic Production of Biodiesel with Acid-Base Bifunctional Rod-Like Ca-B Oxides by the Sol-Gel Approach

The search for acid-base bifunctional catalysts has become a hot topic in the preparation of biofuels from renewable resources. In the present work, a series of novel acid-base bifunctional metal-boron catalysts were successfully prepared by a sol-gel method and characterized by XRD, IR, SEM, TEM, TGA, BET, and TPD. Among those bifunctional solid materials, the Ca-B(700) catalyst had the highest density of both acid and base sites and showed excellent catalytic performance in the production of biodiesel from nonedible oils with high acid value. Under the optimal reaction conditions of 20/1 methanol/oil mole ratio and 4 wt % catalyst dosage at 105 °C for 2 h, a high biodiesel yield of 96.0% could be obtained from Jatropha curcas oil in one-pot. In addition, Ca-B(700) was also applicable to producing biodiesel from Firmiana platanifolia L.f. oil in a relatively low acid value, with an almost quantitative yield (98.5%) at 65 °C after 2 h. The Ca-B(700) catalyst had good stability and reusability, which is a promising acid-base bifunctional catalytic material for the preparation of biodiesel.

Robust Bifunctional Core–Shell MOF@POP Catalyst for One-Pot Tandem Reaction

A new bifunctional acid-base catalyst, core-shell UiO-66@SNW-1, with robust chemical and thermal stability, recyclability, and durable catalytic activity is synthesized by a convenient, universal strategy. Interestingly, this hybrid material can effectively catalyze deacetalization-Knoevenagel condensation reaction in the presence of excellent compartmentalization to spatially isolate opposing acid-base sites.

Acid-Base Bifunctional Metal-Organic Frameworks: Green Synthesis and Application in One-Pot Glucose to 5-HMF Conversion

The direct synthesis of metal-organic frameworks (MOFs) with acidic and basic active sites is challenging due to the introduction of functional groups by post-functionalization method often jeopardize the framework integrity. Herein, we report the direct synthesis of acid-base bi-functional MOFs with tuning acid-base strength. Employing modulated hydrothermal (MHT) approach, microporous MOFs named UiO-66-NH2 was prepared. Through the ring-opening reaction of 1,3-propanesultone with amino group, UiO-66-NH2-SO3H-type catalysts can be obtained. The synthesized catalysts were well characterized and their catalytic performances were evaluated in one-pot glucose to 5-HMF conversion. Results revealed the acid-base bi-functional catalyst possessed high activity and excellent stability. This work provides a general and economically viable approach for the large-scale synthesis of acid-base bi-functional MOFs for their potential use in catalysis field.

Core-shell nanostructured heteropoly acid-functionalized metal-organic frameworks: Bifunctional heterogeneous catalyst for efficient biodiesel production

We developed a new class of acid-base bifunctional heterogeneous catalyst, which can be used in the transesterification of rapeseed oil for highly efficient biodiesel production. A simple Keggin-type HPA (heteropoly acid) functionalization on the surface of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles, through an imidazolium medium, results in the bifunctional heterogeneous catalysts. The hybrid materials exhibit a novel hierarchically core-shell nanostructure, which provides a large surface area and interconnectivity, leading to a thin-wrinkled HPA shell at the surface of rhombic dodecahedral ZIF-8 core crystals. A strong ON hybrid bonding through an electrostatic effect in the hybrid materials demonstrates a strong interaction between the Keggin and imidazole units, which is one of the main driving forces of hybrid materials formation. Additionally, the transformation of the HPA/ZIF-8 ratio in the hybrid materials changes the acidity and basicity, thereby affecting catalyst activity. We used these bifunctional core-shell materials as environmentally friendly heterogeneous catalysts in the transesterification of rapeseed oil with methanol to produce a high-quality biodiesel. Of particular interest, the HPA-functionalized ZIF-8 catalyst with a proper HPA/ZIF-8 ratio shows a high FAME conversion of 98.02% along with high recyclability because of the sufficiently large surface area and bi-functionality of strong acidity. Furthermore, the HPA-functionalized ZIF-8 catalyst shows a high reaction efficiency of the benzyl alcohol oxidation process, indicating a great potential of our catalyst to a wide range of applications.