Base Catalyst Research Articles

Sb-loaded MnOx/TiO2/CNTs catalysts for selective catalytic reduction of NOx: insight to the SO2 and H2O tolerance

PurposeThis paper aims to synthesize and test Mn-Sb/TiO2-CNT catalysts with different Sb/Mn molar ratios to be used in NH3-SCR reaction.Design/methodology/approachA series of Sb-loaded carbon nanotubes (CNTs)-based Mn/TiO2 catalysts were prepared by the incipient wetness co-impregnation method and tested for the selective catalytic reduction (SCR) of NOx with NH3.FindingsThe Sb-loaded Mn/TiO2-CNTs catalyst outperformed other catalysts and presented the highest activity in the temperature regime of 100–400°C. The catalyst loaded with Sb also showed good SO2 and H2O resistance and exhibited better thermal stability. A stepwise study of SO2 addition evidenced that Mn-Sb/TiO2-CNTs catalyst exhibited better SO2 resistance than the base catalyst Mn/TiO2, where the Sb doping greatly inhibited the sulphating of active phase of the catalyst.Originality/valueIn Sb-loaded catalysts, the formed SOx species fused with SbOx instead of MnOx. This favoured interaction of SO2 with SbOx successfully prevents the MnOx from being sulphated by SO2 which substantially improves the SO2 tolerance of Sb-loaded catalysts.

Proton transfer anionic polymerization with C-H bond as the dormant species.

Living anionic polymerization-the most common living polymerization and the one with the longest history-generally requires stringent, water-free conditions and one metal initiator per polymer chain. Here we present the proton transfer anionic polymerization of methacrylates using acidic C-H bonds as the dormant species that are activated by base catalysts. The polymerization mechanism involves reversible chain transfer or termination of the growing enolate species. A weakly acidic compound, such as an alkyl isobutyrate, serves as the initiator or chain-transfer agent in the presence of a bulky potassium base catalyst to produce a polymer chain and, thereby, diminishes the metal compound per chain ratio. An added alcohol serves as a reversible terminator to tame the propagation. End-functionalized, star, block and graft polymers are easily accessible from compounds with C-H bonds.

Liquid-Liquid Equilibrium of Sesame Fatty Acid (Ethyl and Methyl) Ester + Glycerol + Ethanol/Methanol Mixtures at Different Temperatures.

This study aimed to investigate the liquid-liquid equilibrium (LLE) behavior of sesame fatty acid ethyl ester (FAEE) and methyl ester (FAME) in combination with glycerol and the co-solvents ethanol and methanol. FAEE and FAME were produced through the transesterification of mechanically extracted and purified sesame oil, using potassium hydroxide (KOH) as a homogeneous base catalyst. The reactions were conducted in ethanol and methanol to produce FAEE and FAME, respectively. Post-reaction, the products were separated and purified, followed by an analysis of the LLE behavior at 313.15 K and 323.15 K under atmospheric pressure (101.3 kPa). The experimental process for the miscibility analysis utilized a jacketed glass cell adapted for this study. Miscibility limits or binodal curves were determined using the turbidity-point method. Tie lines were constructed by preparing mixtures of known concentrations within the two-phase region, which allowed the phases to separate after agitation. Samples from both phases were analyzed to determine their composition. This study revealed that higher temperatures promoted greater phase separation and enhanced the biodiesel purification process. The NRTL model effectively correlated the activity coefficients with the experimental data, showing good agreement, with a root-mean-square deviation of 3.5%. Additionally, the data quality was validated using Marcilla's method, which yielded an R2 value close to 1. Attraction factors and distribution coefficients were also calculated to evaluate the efficiency of the co-solvents as extraction agents. The findings indicated higher selectivity for methanol than for ethanol, with varying degrees of distribution among the co-solvents. These results offer significant insights into enhancing biodiesel production processes by considering the effects of co-solvents on the LLE properties of mixtures, ultimately contributing to more efficient and cost-effective biodiesel production.

Production of Biodiesel from Crude Pittosporum resiniferum Oil Using Heterogeneous Solid Base Catalyst

ABSTRACTPittosporum resiniferum oil was extracted from the seed and the oil together with methanol was use for the production of biodiesel through transesterification process using novel solid base catalyst (K2CO3 supported on MgO). 0.6:5 (K2CO3 loaded on MgO), a 5 h calcination time, 600°C calcination temperatures were the optimum conditions under which the catalyst was prepared. FTIR, SEM, CO2‐TPD, XRD, N2 adsorption‐desorption, Hammett indicators and other techniques were used to characterize the catalyst. The molar ratio of methanol‐to‐oil, the catalyst amount, time of the reaction as well as the temperature of the reaction were examined. The study found that 16:1 methanol‐to‐oil molar ratio, 5% catalyst loading amount, a reaction time of 2.0 h, and a reaction temperature of 60°C were sufficient for a maximum yield of 97.4%. With relative high activity, the catalyst can perhaps be used again possibly for five times. The characteristics of the biodiesel produced were consistent with international standards.

Revisiting hydrotalcite synthesis: Efficient combined mechanochemical/coprecipitation synthesis to design advanced tunable basic catalysts

Abstract Hydrotalcite materials (HTs) were synthesized by a facile and swift combined mechanochemistry/coprecipitation approach, and their catalytic activity was evaluated and compared with conventionally synthesized hydrotalcites (co-precipitation method) in the Knoevenagel condensation between furfural and ethyl cyanoacetate/malononitrile. Characterization and catalytic activity results clearly demonstrate that the proposed combined mechanochemical/coprecipitation approach provides an improvement in crystallinity, morphology, tunable basicity, and textural properties (higher surface area and enhanced surface properties) as compared to HTs obtained via conventional coprecipitation methods. In addition, mechanochemically synthesized HTs largely improve catalytic activities, including conversion and product selectivity to Knoevenagel condensation products under solventless conditions, short reaction times, or reaction at room temperature as compared to conventional counterparts (e.g., 30–40 vs > 99% product yields).

Talc: A natural mineral base catalyst for the one pot synthesis of bis(pyrazolyl)methane derivatives under thermal and solvent-free conditions

In this work, we were decontaminated the ore to extract the talc, directly. Then, we used talc as a heterogeneous basic catalyst for one pot synthesis of bis(pyrazolyl)methane derivatives via the condensation of ethylacetoacetate, hydrazine hydrate and aromatic aldehyde derivatives under thermal and solvent-free conditions. This solid type of catalyst was identified by fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), EDS mapping and Brunauer–Emmett–Teller (BET) theory. Heterogeneous and solvent-free conditions, catalyst recyclability, high yields of the products and short reaction times are some advantages of this method. The reusability of the catalyst was examined for five times and it was successfully used in each run without any significant decreasing in its activity.

Facile Access to Organostibines via Selective Organic Superbase Catalyzed Antimony‐Carbon Protonolysis

AbstractThe selective formation of antimony‐carbon bonds via organic superbase catalysis under metal‐ and salt‐free conditions is reported. This novel approach utilizes electron‐deficient stibine, Sb(C6F5)3, to give upon base‐catalyzed reactions with weakly acidic aromatic and heteroaromatic hydrocarbons access to a range of new aromatic and heteroaromatic stibines, respectively, with loss of C6HF5. Also, the significantly less electron‐deficient stibines, Ph2SbC6F5 and PhSb(C6F5)2 smoothly underwent base‐catalyzed exchange reactions with a range of terminal alkynes to generate the stibines of formulae PhSb(C≡CPh)2, and Ph2SbC≡CR [R=C6H5, C6H4‐NO2, COOEt, CH2Cl, CH2NEt2, CH2OSiMe3, Sb(C6H5)2], respectively. These formal substitution reactions proceed with high selectivity as only the C6F5 groups serve as a leaving group to be liberated as C6HF5 upon formal proton transfer from the alkyne. Kinetic studies of the base‐catalyzed reaction of Ph2SbC6F5 with phenyl acetylene to form Ph2SbC≡CPh and C6HF5 suggested the empirical rate law to exhibit a first‐order dependence with respect to the base catalyst, alkyne and stibine. DFT calculations support a pathway proceeding via a concerted σ‐bond metathesis transition state, where the base catalyst activates the Sb‐C6F5 bond sequence through secondary bond interactions.

Facile Access to Organostibines via Selective Organic Superbase Catalyzed Antimony-Carbon Protonolysis.

The selective formation of antimony-carbon bonds via organic superbase catalysis under metal- and salt-free conditions is reported. This novel approach utilizes electron-deficient stibine, Sb(C6F5)3, to give upon base-catalyzed reactions with weakly acidic aromatic and heteroaromatic hydrocarbons access to a range of new aromatic and heteroaromatic stibines, respectively, with loss of C6HF5. Also, the significantly less electron-deficient stibines, Ph2SbC6F5 and PhSb(C6F5)2 smoothly underwent base-catalyzed exchange reactions with a range of terminal alkynes to generate the stibines of formulae PhSb(C≡CPh)2, and Ph2SbC≡CR [R=C6H5, C6H4-NO2, COOEt, CH2Cl, CH2NEt2, CH2OSiMe3, Sb(C6H5)2], respectively. These formal substitution reactions proceed with high selectivity as only the C6F5 groups serve as a leaving group to be liberated as C6HF5 upon formal proton transfer from the alkyne. Kinetic studies of the base-catalyzed reaction of Ph2SbC6F5 with phenyl acetylene to form Ph2SbC≡CPh and C6HF5 suggested the empirical rate law to exhibit a first-order dependence with respect to the base catalyst, alkyne and stibine. DFT calculations support a pathway proceeding via a concerted σ-bond metathesis transition state, where the base catalyst activates the Sb-C6F5 bond sequence through secondary bond interactions.

An eco-friendly and new facile method for synthesis of prenylated or geranylated acylphloroglucinol-based xanthenones

The synthesis of prenylated or geranylated acylphloroglucinol-based xanthenones with 15.1–36.9% yield was achieved via aldol condensation of 2,4,6-trihydroxy-3-prenylacetophenone (tHPA) or 2,4,6-trihydroxy-3-geranylacetophenone (tHGA) and 2-hydroxybenzaldehyde derivatives in the presence of lithium bis(trimethylsilyl)amide (LiHMDS) as deprotonating agent. This study is one of the first to report on the synthesis of xanthenones using strong non-nucleophilic base catalyst, and the described synthesis not only achieved a compound with a natural product skeleton but also formed in a simple and environmentally friendly specificity.

Efficient Photocatalytic System based on Schiff‐Base Type Hybrid Polymers for Energy Conversion and Water Treatment

AbstractIn this contribution, a new Schiff‐base hybrid cross‐linked polymer (TFPT‐SHCP) derived from triazine derivatives and silsesquioxanes was developed, and its photocatalytic performance was systematically investigated. Compared with traditional organic Schiff base catalysts, in TFPT‐SHCP, organic inorganic hybrid silsesquioxanes monomers at the molecular level can serve as a sturdy host backbone, bringing structural ultrastability to the final material. And their excellent strength and durability make them have good application prospects in water treatment. Furthermore, the introduction of triazine derivatives with excellent photoelectric performance and the construction of −C=N‐ result in excellent photocatalytic performance of TFPT‐SHCP. The as‐prepared TFPT‐SHCP exhibits excellent degradation capacity of various organic pollutants under visible light catalysis, with degradation rate constants for Congo Red (CR), rhodamine B (RB) and tetracycline hydrochloride (TH) reaching 0.302 min−1, 0.121 min−1, 0.161 min−1, respectively. Under simulated outdoor conditions, dye solutions with concentrations up to 500 ppm can be degraded to complete decolorization within 5 weeks. This work demonstrates the enormous potential of POSS‐based Schiff base materials as a platform for visible light catalysts, paving the way for the pre design and functionalization of related materials in the future.

Nickel-chelatase activity of SirB variants mimicking the His arrangement in the naturally occurring nickel-chelatase CfbA.

Metal-tetrapyrrole cofactors are involved in multiple cellular functions, and chelatases are key enzymes for the biosynthesis of these cofactors. CfbA is an ancestral, homodimeric-type class II chelatase which is able to use not only Ni2+ as a physiological metal substrate, but also Co2+ as a nonphysiological substrate with higher activity than for Ni2+. The Ni/Co-chelatase function found in CfbA is also observed in SirB, a descendant, monomeric-type class II chelatase. This is despite the distinct active site structure of CfbA and SirB; specifically, CfbA shows a unique four His residue arrangement, unlike other monomeric class II chelatases such as SirB. Herein, we studied the Ni-chelatase activity of SirB variants R134H, L200H, and R134H/L200H, the latter of which mimics the His alignment of CfbA. Our results showed that the SirB R134H variant exhibited the highest Ni-chelatase activity among the SirB enzymes, which in turn suggests that the position of His134 could be more important for the Ni-chelatase activity than that of His200. The SirB R134H/L200H variant showed lower activity than R134H, despite the four His residues found in SirB R134H/L200H. CD spectroscopy showed secondary structure denaturation and a slight difficulty in Ni-binding of SirB R134H/L200H, which may be related to its lower activity. Finally, a docking simulation suggested that the His134 of the SirB R134H variant could function as a base catalyst for the Ni-chelatase reaction in a class II chelatase architecture.

LaMn1-xCoxO3 perovskite-like doped and impregnated with Cu for the enhancement of toluene total oxidation

Perovskite-like materials have gained great interest and importance due to their wide range of applications, especially in the context of the world of sustainability. In this study, the effect of copper on the catalytic performance of LaMn1-xCoxO3 perovskite-like oxides towards toluene oxidation was investigated. Preliminary activity results indicated that perovskites with higher Mn content or x = 0.0 and 0.25, (LM = LaMnO3 and LMC = LaMn0.75Co0.25O3), could be selected as base catalysts to evaluate the copper addition either by structural doping or surface impregnation. It was found that Cu-impregnated catalysts (Cu[x]/LM and Cu[x]/LMC) exhibited better catalytic activity towards toluene oxidation compared to Cu-doped catalysts (LM-Cu[x] and LMC-Cu[x]), achieving total oxidation temperatures below 300 °C. It was found that copper appeared in the impregnated perovskite catalysts in the form of CuO, which is also an active species for toluene oxidation. While, in the Cu-doped catalysts, the CuO segregation was not seen, which could partly explain the low catalytic efficiency of these solids. From the evaluated perovskites, the most active ones against toluene oxidation were Cu[0.3]/LM and Cu[0.4]/LMC, which curiously showed two different oxidation mechanisms for toluene oxidation, the first followed a suprafacial (surface oxygen) mechanism, while the second followed an intrafacial (network oxygen) mechanism.

Design, Preparation, and Implementation of Axially Chiral Benzotetramisoles as Lewis Base Catalysts for Asymmetric Cycloadditions

AbstractDeveloping novel catalysts with potent activity is of great importance in organocatalysis. In this study, we designed and prepared a new class of benzotetramisole Lewis base catalysts (AxBTM) that have both central and axial chirality. This unique feature of these catalysts results in a three‐dimensional microenvironment with multi‐layers of chirality. The performance of the developed catalysts was tested in a series of cycloaddition reactions. These included the AxBTM‐catalyzed (2+2) cycloaddition between α‐fluoro‐α‐aryl anhydride with imines or oxindoles, and the sequential gold/AxBTM‐catalyzed (4+2) cycloaddition of enynamides with pentafluorophenyl esters. The interplay between axial and central chirality had a collaborative effect in regulating the stereochemistry in these cycloadditions, leading to high levels of stereoselectivity that would otherwise be challenging to achieve using conventional BTM catalysts. However, the (2+2) and (4+2) cycloadditions have different predilections for axial and central chirality combinations.

Design, Preparation, and Implementation of Axially Chiral Benzotetramisoles as Lewis Base Catalysts for Asymmetric Cycloadditions.

Developing novel catalysts with potent activity is of great importance in organocatalysis. In this study, we designed and prepared a new class of benzotetramisole Lewis base catalysts (AxBTM) that have both central and axial chirality. This unique feature of these catalysts results in a three-dimensional microenvironment with multi-layers of chirality. The performance of the developed catalysts was tested in a series of cycloaddition reactions. These included the AxBTM-catalyzed (2+2) cycloaddition between α-fluoro-α-aryl anhydride with imines or oxindoles, and the sequential gold/AxBTM-catalyzed (4+2) cycloaddition of enynamides with pentafluorophenyl esters. The interplay between axial and central chirality had a collaborative effect in regulating the stereochemistry in these cycloadditions, leading to high levels of stereoselectivity that would otherwise be challenging to achieve using conventional BTM catalysts. However, the (2+2) and (4+2) cycloadditions have different predilections for axial and central chirality combinations.

Synthesis of reactive trichloroacetimidates using polymer supported DBU catalysis

Trichloroacetimidates are commonly synthesized to be used as alkylating or glycosylating reagents. They are synthesized from an alcohol and trichloroacetonitrile and DBU is the preferred base catalyst for this reaction. Here is presented a method, where commercially available solid supported DBU (PS-DBU) is used as the catalyst (3–8 mol%) resulting in a less discolored reaction and a simpler isolation of labile products by filtration and concentration, avoiding workup and chromatography. Small volatile trichloroacetimidates can hence be synthesized in an advantageous and economical way.

Enhanced CO2 absorption in amine-based carbon capture aided by coconut shell-derived nitrogen-doped biochar

The sluggish CO2 absorption kinetics and constrained CO2 absorption capacity diminish the practicality of using amine-based absorption for CO2 capture, impeding progress toward carbon neutrality goals. This study aims to develop a catalytic CO2 absorption process to promote CO2 absorption by introducing a solid base catalyst, namely, coconut shell-derived nitrogen-doped biochar (NBC), into an amine-based solution. The coconut shells were modified with urea and activated with KOH to prepare an NBC catalyst with improved basic characteristics. The findings showed that compared to non-catalytic absorption, the NBC catalyst increased the CO2 absorption amount, CO2 absorption rate, and absorption efficiency of the monoethanolamine (MEA) solution by 16.9 %, 43.4 %, and 13.1 %, respectively. The basic sites on the NBC surface provided extra electrons to motivate the formation of MEACOO- and HCO3-. NBC’s large surface area and porous structure also advanced the gas–liquid mass transfer, accelerating the CO2 absorption rate. Furthermore, the NBC exhibited excellent cyclic stability and facilitated the subsequent CO2 desorption process. This work develops a promising and practical approach to significantly improve the amine-based absorption and reuse of waste biomass resources for efficient CO2 capture.

NaAlO2/CuFe2O4 as a novel basic magnetic heterogeneous catalyst for effective biodiesel production: Synthesis, characterization, and optimization via RSM-FCCD modeling approach

This research focus on the development of a novel and superior basic magnetic heterogeneous catalyst, using NaAlO2 as an active species supported in CuFe2O4 to produce biodiesel. Thus, a series of catalysts have been synthesized by means of conventional and low-cost methods. The features of catalyst have been elucidated through techniques such as basicity, XRD, FTIR, SEM, EDS, TG/DTG and VSM. To optimize the biodiesel’s ester content, the face-centered central composite design with the response surface methodology, was employed to assess the effect of the aspects on the process: reaction temperature, MeOH:oil molar ratio, catalyst dosage and time. The regression model presented R2 = 0.9394 and experimentally reached a maximum ester content of 95.9 % attributed to the biodiesel attained under the optimal reaction conditions: temperature of 95.0 °C, MeOH:oil molar ratio of 13:1, catalyst dosage of 8.0 % and time of 60.0 min. The catalyst presented a stable catalytic performance during four transesterification cycles (>90.0 %) and an efficient magnetic property for the catalyst separation and recovery process (Ms = 23.62 emu g−1). The biodiesel’s physicochemical properties were in compliance with ASTM D6751 standard. Finally, this extensive study reveals the basic magnetic heterogeneous catalyst as a practical and promising alternative to produce a sustainable biofuel.

Chiral Brønsted Base Activation of Donor-Acceptor Cyclopropanes toward Diastereo- and Enantioselective [3 + 2] Cycloaddition with Isatin-Derived Ketimines.

Organocatalyzed diastereo- and enantioselective [3 + 2] cycloaddition reactions of donor-acceptor (D-A) cyclopropanes with isatin-derived ketimines are presented. Different from well-developed Lewis acid activation protocols which promote the reactivity of D-A cyclopropanes through coordinating to the acceptor group, in this reaction, dicyanocyclopropylmethyl ketones can be activated through nucleophilic activation of the donor group by using dihydroquinine-derived squaramide as Brønsted base catalyst. The reaction affords functionalized spiro[oxindole-3,2'-pyrrolidines] with two nonadjacent tetra- and tri-substituted stereocenters in 83-99% yields, moderate to excellent diastereoselectivities (up to >20:1 diastereomeric ratio (dr)), and excellent enantioselectivities (up to >99% enantiomeric excess (ee)) under mild conditions.

Sonochemical synthesis of hollow mesoporous silica spheres (HMSSs) and its effective utilization for one-step synthesis of curcumin-loaded HMSSs

Herein, HMSSs were successfully synthesized using the sonochemical method. Compared with a conventional synthesis under continuous stirring, HMSSs synthesized under ultrasound irradiation were uniform hollow spheres with a thinner mesoporous shell, resulting in higher pore volumes and larger specific surface areas. The hollow cores were acquired without the templates but from ethanol droplets generated in situ by ultrasound. The ethanol/water volume ratio (E/W) affected the structures of sonochemical synthesized particles, i.e., mesoporous silica particles were obtained at low E/W before transforming to HMSSs under moderate E/W and dense silica spheres at high E/W. Varying [NH4OH] base catalysts in an aqueous phase altered the core structure of HMSSs from hollow cores at high [NH4OH] to partial-filled cores at a moderate concentration and non-hollow cores at low [NH4OH]. Ultrasound was effectively utilized to prepare curcumin-loaded HMSSs in a single step. Stable ethanol droplets containing curcumin were produced from the ultrasound's homogenizing effect, leading to curcumin's encapsulation within HMSSs. While the cavitation induced the chemical effect, reducing the reaction time. The encapsulation of curcumin and the formation of HMSSs could occur concurrently; thus, not only is the drug loading step unnecessary, but the efficiency of loading drugs inside HMSSs is also enhanced.

One pot, two-step synthesis of 2-(subs.)-1H-benzimidazoles using wet copper slag as magnetically separable and recyclable catalyst

This work describes the first-ever use of Wet copper slag for 2-(subs.)-1H-benzimidazoles synthesis. It is a by-product of the copper refining and smelting processes utilized as a basic catalyst in the present work. Wet copper slag is prepared by immersing a natural copper slag in water to improve the hydroxyl group and, hence, basicity. Iron oxide content in the copper slag helps provide the basic environment and uses surrounding air for the successful oxidative condensation of imines and o-phenylenediamine. Various aldehydes reacted well with p-anisidine for imine synthesis. Further reaction with substituted o-phenylenediamine and o-phenylenediamine gives desired 2-(subs.)-1H-benzimidazoles in environmental-friendly ethanol: water (9:1) as solvent at 85 °C within 40 to 60 min. The present method showed critical advantages of mild reaction conditions, wide availability, recyclability, and magnetic separability of a Copper-slag with moderate to excellent product yields. Overall, the present approach offers a promising route for the efficient and sustainable synthesis of 2-(subs.)-1H-benzimidazoles, which have a wide range of applications in various fields, including pharmaceuticals, agrochemicals, and materials science.