Esterification Of Free Fatty Acids Research Articles

Synthesis of MgO/MgSO4 nanocatalyst by thiourea–nitrate solution combustion for biodiesel production from waste cooking oil

A novel MgO/MgSO4 nanocatalyst was synthesized using solution combustion method with thiourea as the fuel. The in-situ inducement of sulfonated group over the basic catalyst, MgO, was carried out for the first time using thiourea for the production of biodiesel. The synthesized nanocatalyst with its bi-functional characteristics performed efficiently in the simultaneous transesterification and esterification of high free fatty acid (FFA) containing waste cooking oil (WCO) into biodiesel in the presence of ultrasound. The newly developed nanocatalyst was characterized by XRD, FESEM, EDS, FTIR and BET analyses. The resulting nanocatalyst possesses a specific surface area of 82 m2/g and a pore volume of 0.047 cm3/g. The high sulfur content of 13.65% of the novel catalyst developed facilitates its high acidic characteristics suitable for the esterification step. The optimization of the process carried out by the response surface methodology (RSM) predicted the optimized parameters as follows: methanol to oil molar ratio-9.4:1, catalyst loading-8.9 wt%, ultrasonic power-402 W and reaction time-46 min. The optimum yield of biodiesel predicted by the RSM was 98.8%. The synthesized nanocatalyst demonstrated high stability which established significant future perspective for industrial production of biodiesel from low cost, high FFA containing feedstock.

Combination of Biocatalysis and Sonochemistry in the Ethyl Oleate Production

Objectives:Fatty acid alkyl esters (FAAEs) are a family of natural neutral lipids and can be produced cleanly and sustainably by esterification of free fatty acids (FFAs) with short chain alcohol using enzymatic catalysts. In this study, the use of lipases was evaluated in enzymatic esterification of oleic acid with ethanol using the combination of biocatalysis and sonochemistry (ultrasound) in the absence of co-solvents.Methods:Reaction parameters, such as type of lipase, amount of enzyme, reaction time, alcohol hydration level and enzyme turnover were evaluated for the enzymatic synthesis of ethyl oleate.Results:C. antarctica lipase provided yields above 95% in less than 10 h with 10% (w/w) of lipase. The use of hydrous ethanol (5% of water) showed a slight drop in yield but remained above 90% of ethyl oleate production. C. antarctica lipase showed no loss efficiency even after 10 reaction cycles.Conclusion:The combination of biocatalysis and ultrasound radiation provided a high yield, showing that the combination of these tools may be a good choice for the enzymatic synthesis of ethyl oleate.

Decyl esters production from soybean-based oils catalyzed by lipase immobilized on differently functionalized rice husk silica and their characterization as potential biolubricants

This study aimed the enzymatic decyl esters production by hydroesterification, a two-step process consisting of hydrolysis of refined soybean (RSBO) or used soybean cooking (USCO) oils to produce free fatty acids (FFA) and further esterification of purified FFA. Using free lipase from Candida rugosa (CRL), about 98% hydrolyses for both oils have been observed after 180 min of reaction using a CRL loading of 50 U g–1 of reaction mixture, 40 °C, and a mechanical stirring of 1500 rpm. FFA esterification with decanol in solvent-free systems was performed using lipase from Thermomyces lanuginosus (TLL) immobilized by physical adsorption on silica particles extracted from rice husk, an agricultural waste. For such purpose, non-functionalized (SiO2) or functionalized rice husk silica bearing octyl (Octyl–SiO2) or phenyl (Phe–SiO2) groups have been used as immobilization supports. Protein amounts between 22 and 28 mg g–1 of support were observed. When used in the esterification, they enabled a FFA conversion of 81.3–87.6% after 90–300 min of reaction. Lipozyme TL IM, a commercial immobilized TLL, exhibited similar performance compared to TLL–Octyl–SiO2 (FFA conversion ≈90% after 90–120 min of reaction). However, high operational stability after fifteen successive esterification batches was observed only for TLL immobilized on Octyl–SiO2 (activity retention of ≈90% using both FFA sources). The produced decyl esters presented good characteristics as potential biolubricants according to standard methods (ASTM) and thermal analysis.

Application of acidic ionic liquids for the treatment of acidic low grade palm oil for biodiesel production

Employing low quality feedstocks for biodiesel production can present cost reduction opportunities due to its wide availability and cost effectiveness. However, most low quality feedstocks have high free fatty acid (FFA) content which is not feasible for biodiesel production through direct transesterification due to soap formation. Thus, a pre-treatment step through FFA esterification could reduce the FFA content while simultaneously yielding fatty acid methyl esters (FAME). In this study, the catalytic activity of ten ionic liquids (ILs) were screened for the esterification of FFA in acidic crude palm oil (ACPO). 1‑butyl‑3-methylimidazolium hydrogen sulfate as IL exhibited the highest catalytic activity and was further investigated to determine the optimum operating parameters such as IL dosage, molar ratio, reaction temperature and time. Single factor optimization was employed for the laboratory scale batch esterification reaction. The FFA content was reduced from 10.77% to less than 1% using the following optimum conditions: 4% IL to oil, molar ratio of 10:1 (methanol to oil), 120 min reaction time and 60 °C reaction temperature. Under optimum conditions, the IL can be recycled five times with minimal loss in catalytic activity, highlighting its feasibility as an industrial catalyst for esterification of acidic oils and fats.

Lewatit-immobilized lipase from Bacillus pumilus as a new catalyst for biodiesel production from tallow: Response surface optimization, fuel properties and exhaust emissions

Biodiesel is currently regarded as a sustainable and renewable alternative to depleting fossil fuels such as petro-diesel. Biodiesel production on a large scale could have a positive impact on the energy sector and the environment by lowering greenhouse gas emissions. Disadvantages of biodiesel include utilization of high-cost edible oils for production of biofuels, generation of wastewater and inability to recycle catalysts after alkaline-catalyzed methanolysis. The objectives of the current study were to utilize low-cost, inedible tallow to produce biodiesel from Lewatit-immobilized lipase produced from Bacillus pumilus and to measure the fuel properties and exhaust emissions of the resulting fatty acid methyl esters. Response surface methodology was used to optimize reaction conditions and alkaline (potassium hydroxide; KOH) catalysis was performed for comparison. A conversion of 96% was achieved by two step chemical-mediated transesterification, whereas conversion was 67% for the single step lipase-mediated method. Acid pre-treatment was needed in the case of KOH-catalyzed transesterification to reduce the acid value of tallow from 17.6 to 1.3 mg KOH/g, whereas the Lewatit-immobilized lipase was able to efficiently catalyse both transesterification of glycerides and esterification of free fatty acids. To the best of our knowledge, the lipase from B. pumilus has not yet been studied for biodiesel production from tallow. Fuel properties of the resulting optimized biodiesel were within the limits prescribed in ASTM D6751 and EN 14214. In addition, exhaust emissions studies revealed reduced CO and PM relative to petro-diesel. In both cases, reductions were greater as the percentage of biodiesel increased in blends with petro-diesel. However, NOx emissions were elevated versus petrodiesel in blends that contained 50% or more of biodiesel. This research reveals new ways for utilization of waste animal fats for biodiesel production as well as a new efficient lipase source that yields more products and provides environmental and economic security.

Molybdenum and zirconium oxides supported on KIT-6 silica: A recyclable composite catalyst for one–pot biodiesel production from simulated low-quality oils

The development of feasible ecofriendly processes for biodiesel production is highly desirable to meet the requirement of green chemistry and sustainable development. To reach this goal, the molybdenum and zirconium oxides were incorporated into commercial available KIT-6, mesoporous silica nanoparticle, by a solvothermal method, to form MoO3/ZrO2/KIT-6 catalyst. The targeted solid composite catalysts were structurally characterized using XRD, TEM, SEM, XPS, EDS, TG, and nitrogen porosimetry measurement. The characterization results showed that the ordered porous structure of the support was well persevered with high surface area, and the molybdenum and zirconium oxides could be highly dispersed on the mesoporous support. The acidic nature of the solid catalyst was evaluated in detail by means of NH3-TPD and infrared spectra of adsorbed pyridine techniques. It was indicated that the acidities of the solid catalysts, with both Brønsted and Lewis acid sites, could greatly affected their catalytic activity. This catalyst displayed high activities to the transesterification of triglycerides and esterification of free fatty acids (FFAs) simultaneously owing to the synergistic effect of Brønsted and Lewis acid sites, thus achieving one-pot heterogeneous production of biodiesel as the low-quality oil was used as feedstocks. The influence of reaction parameters and the catalyst reusability were also investigated, and the best oil conversion of 92.7% was obtained under the optimized reaction conditions. The targeted catalyst exhibited a better FFAs and water tolerant for the reaction, advantageously with no noticeable decline in the catalytic performance even after five reaction cycles.

Heterogeneous H6PV3MoW8O40/AC-Ag catalyst for biodiesel production: Preparation, characterization and catalytic performance

The heterogenization of Keggin-structure heteropoly acids (HPAs) has been proposed as a strategy to improve their application in biodiesel production in an attempt to comply the green and clean production demand. Herein, the commercial activated carbon (AC) was firstly modified with different metal ions (Cs+, K+ and Ag+), and then the H6PV3MoW8O40 acid was incorporated into as-modified AC supports, so as to prepare HPAs-based solid catalysts. By screening tests, the 35%H6PV3MoW8O40/AC-Ag hybrid solid catalyst showed highly catalytic performance for transesterification of soybean oil. The best oil conversion of 91.3% was achieved under optimized conditions: methanol/oil molar ratio of 30:1, reaction time of 10 h, reaction temperature of 140 °C and catalyst dosage of 8 wt.%. Characterization results of XRD, IR, ICP and TG indicated that H6PV3MoW8O40 was highly dispersed on the AC-Ag support as the loading was less than 35%. Proton exchange with Ag may contribute to the highly dispersion of H6PV3MoW8O40 on the support and thus enhance the interaction of the heteropoly acids with the support, thereof leading to the increased catalytic stability. The as-prepared 35%H6PV3MoW8O40/AC-Ag catalyst was easily recycled and had good resistance to free fatty acid (FFA) and water, which were usually included in the low-quality oils. Moreover, as a bifunctional catalyst, the solid acid catalyst could simultaneously catalyze the transesterification of soybean oil and esterification of FFAs, and a probable mechanism of the catalytic process was also proposed. All the features of this novel solid catalyst are more advantageous than the homogenous H6PV3MoW8O40 catalyst, successfully creating an efficient and sustainable approach of biodiesel production especially from the low-quality oils.

Esterification of Free Fatty Acid in Palm Oil Mill Effluent using Sulfated Carbon-Zeolite Composite Catalyst

Free fatty acid esterification (FFA) in palm oil mill waste (POME) was carried out using a sulfonated carbon-zeolite composite catalyst. The catalyst is synthesized with carbon precursor obtained from molasses, which is adsorbed on the surface of the zeolite and then carbonized and sulfonated with concentrated H2SO4 to form a sulfonated carbon-zeolite catalyst composite, which will be used for the esterification catalyst and the optimization process for the esterification reaction is carried out using the response surface methodology (RSM) and experimental central composite design (CCD). Importantly, the observed independent variables were temperature, catalyst weight, and reaction time to produce fatty acid methyl ester (FAME) products. The catalyst was successfully synthesized, which was shown from the SEM characterization strengthened by the presence of a sulfate group in the FTIR results and the calculation results of high acidity properties. Optimization of FFA esterification with SCZ catalyst obtained optimal conditions with a temperature of 79oC, a catalyst weight of 3.00 g, and a reaction time of 134 minutes with a FAME product of 93.75%, considering that the viscosity of biodiesel is below that required by the API.

Transesterification Studies on Avocado Seed Oil Using Carbon Supported CuO Nano Catalyst: Rate Kinetics and Thermodynamic Aspects

This study focused on the production of biodiesel using avocado seed oil (ASO) through esterification of free fatty acids (FFA) in the presence of carbon supported CuO nanoparticles (CuO/C). ASO was obtained using hexane as a solvent by Soxhlet extraction. Further characterization of ASO revealed that the oil had 8.2‐10.2% (±0.2%) of FFA content. Using a two‐step technique, the FFA content was decreased below 1% through esterification using a catalyst prepared from carbon supported nanoparticles of CuO. Additionally, CuO/C catalyst was characterized by different techniques, such as XRD and BET. From the investigations, the optimal time for the esterification process was found to be 6 h at 673 K. The use of carbon supported CuO nanoparticle for the transesterification process of ASO has not been attempted in earlier. Also, the studies on FFA present in the avocado seed oil had a significant outcome in this investigation. Further, the data observed from the reactions conducted at different temperatures were subjected for kinetic analysis to determine the reaction rate and thermodynamic study for activation energy.

Obtention of biodiesel through an enzymatic two-step process. Study of its performance and characteristic emissions.

We describe the enzymatic synthesis of biodiesel from waste cooking oil (WCO) in a two-step production process: hydrolysis of WCO, followed by acid-catalyzed esterification of free fatty acids (FFAs). Among the three commercial enzymes evaluated, the inexpensive lipase Lipex® 100L supported on Lewatit® VP OC 1600 produced the best overall biodiesel yield (96.3%). Finally, we assessed the combustion efficiency of the obtained biodiesel and its blends. All blends tested presented lower emissions of CO and HC compared to diesel. The NOx emissions were higher due to biodiesel's high volatility and viscosity. The cost of biodiesel production was calculated using the process described.

Novel self-solidifying double-site acidic ionic liquid as efficient and reusable catalyst for green biodiesel synthesis

In this work, two double-site acidic ionic liquids were synthesized by a two-step method via the reaction of 1,2-bis(diphenylphosphino) ethane (DPhPE) with 1,3-propanesulfonate (PS) to form a DPhPE-PS zwitterion followed by acidification with different acids. The obtained ionic liquids were characterized and further used as catalyst for the esterification of various free fatty acids with methanol to produce biodiesel. The suitable self-solidifying double-site acidic ionic liquid [DPhPE-PS][HSO4]2 is homogeneous catalytic due to its solubility during the esterification, which is precipitated after reaction. The evaporation of the residual methanol and generated water combines the advantages of homogeneous and heterogeneous catalysts, including their excellent catalytic activity and convenient recovery. [DPhPE-PS][HSO4]2 exhibits 98.65% of oleic acid conversion under operating appropriate conditions optimized by response surface methodology (catalyst dosage of 6.0 wt%, molar ratio of methanol to oleic acid of 10.0:1, reaction temperature of 60.0 °C, and reaction time of 4.0 h) and keeps outstanding catalytic performance after 9 cycles. Moreover, [DPhPE-PS][HSO4]2 also displays excellent catalytic activity and good versatility in the esterification of various free fatty acids to biodiesel. Hence, the self-solidifying double-site acidic ionic liquid [DPhPE-PS][HSO4]2 can be used as an environmentally friendly and efficient catalyst for synthesis of biodiesel via esterification.

Kinetic model for the esterification of free fatty acids from palm oil with methanol using sulfuric acid as catalyst and sensitivity analysis in tubular reactors

AbstractIndustrial biodiesel production from crude palm oil (CPO) by homogeneous transesterification requires some conditioning stages. One is deodorization, where free fatty acids (FFA) are stripped out from the CPO. The FFA from the deodorizer is esterified using a homogeneous acid catalyst to produce more biodiesel and improve process profitability. This work studied the sulfuric acid‐catalyzed esterification of FFA with methanol. The factors evaluated were temperature (between 40 and 60°C) and catalyst concentration (between 0.15 and 1.5 wt% based on the mixture). The parameters of a reversible second‐order kinetic model were adjusted from experimental data using a genetic algorithm. The kinetic model, which adequately represents the esterification reaction, according to the Fisher–Snedecor test, was used to perform a sensitivity analysis in isothermal, adiabatic, and non‐isolated continuous tubular esterification reactors using ASPEN HYSYS V10. The results showed that the highest conversion (~96%) was predicted using an isothermal reactor. However, its installation and operational costs could also be the highest. An adiabatic reactor was preferred, which optimal conversion of 94.5% was predicted at temperature, catalyst concentration, residence time, and methanol‐to‐FFA molar ratio of 140°C, 0.3 wt%, 47 min, and 6.7, respectively, its predicted operational cost was 0.63 dollars per biodiesel kilogram. Therefore, the adjusted and validated model has a relevant importance in the biofuel sector, not only in Colombia, but also worldwide.

Encapsulated deep eutectic solvent for esterification of free fatty acid

A novel encapsulated deep eutectic solvent (DES) was introduced for biodiesel production via a two-step process. The DES was encapsulated in medical capsules and were used to reduce the free fatty acid (FFA) content of acidic crude palm oil (ACPO) to the minimum acceptable level (< 1%). The DES was synthesized from methyltriphenylphosphonium bromide (MTPB) and p-toluenesulfonic acid (PTSA). The effects pertaining to different operating conditions such as capsule dosage, reaction time, molar ratio, and reaction temperature were optimized. The FFA content of ACPO was reduced from existing 9.61% to less than 1% under optimum operating conditions. This indicated that encapsulated MTPB-DES performed high catalytic activity in FFA esterification reaction and showed considerable activity even after four consecutive recycling runs. The produced biodiesel after acid esterification and alkaline transesterification met the EN14214 international biodiesel standard specifications. To our best knowledge, this is the first study to introduce an acidic catalyst in capsule form. This method presents a new route for the safe storage of new materials to be used for biofuel production. Conductor-like screening model for real solvents (COSMO-RS) representation of the DES using σ-profile and σ-potential graphs indicated that MTPB and PTSA is a compatible combination due to the balanced presence and affinity towards hydrogen bond donor and hydrogen bond acceptor in each constituent.

A magnetically separable acid-functionalized nanocatalyst for biodiesel production

A robust, magnetically recoverable Fe3O4@SiO2-SO3H core@shell nanoparticulate acid catalyst was successfully synthesized by a stepwise co-precipitation, coating, and functionalization. It was utilized as a heterogeneous catalyst for the transesterification and esterification of triglycerides and free fatty acids in Jatropha curcas oil (JCO) to a fatty acid methyl ester (FAME) mixture. This product conformed to ASTM standards for biodiesel. The as-prepared catalyst had a magnetic saturation of 30.94 emu g−1, surface area of 32.88 m2g−1, acidity of 0.76 mmol g−1, and pore diameter of 3.48 nm. The catalyst showed 98 ± 1% conversion using the optimized reaction conditions of methanol:oil molar ratio of 9:1, 8 wt% catalyst loading, 80 °C, and 3.5 h. The transesterification of JCO to FAME using the present catalyst benefitted from a very low activation energy of 37.0 kJ mol−1. The solid acid catalyst exhibited excellent chemical and thermal stability, and also reusability based on easy separation from the reaction mixture due to its inherently magnetic nature. Modest deterioration in oil conversion after multiple uses was offset by one-pot, quantitative regeneration of catalyst active sites. This enabled identical performance in JCO methyl transesterification and esterification in the 1st and 10th catalytic cycles.

Association between Adiponectin and Insulin Resistance among Sudanese Males with Type 2 Diabetes Mellitus

Background: Adiponectin is associated with improved systemic insulin sensitivity and profound positive effects in adipose tissue, such as increased mitochondrial density in adipocytes, reducing adipocyte size, and effective esterification of free fatty acids on lipid storage The factor performs forward transcriptional regulation. Diabetes and its complications are considered to be one of the main causes of morbidity and mortality worldwide. Aims and objectives: The aim of this study was to correlate serum levels of adiponectin with insulin resistance in Sudanese males' type 2 diabetes mellitus. Design and Methods: A case-control community-based study carried out among 126 patients with T2DM as cases group (mean ages 45.2±5.4 years); and 126 normal healthy individuals as controls group (mean ages 44.7±5.4 years as) in Aldaraga Diabetic Center, Wad Medani, Gezira State, Sudan. About Five mL of fasting venous blood was obtained from all participants. HbA1c, FPG, FPI, serum Adiponectin, and (HOMA)- IR were analyzed. SPSS (v 20.0) was used for data analysis. Results: The mean of serum adiponectin in the cases group (3.03±0.90µg/ml) was lower than the control group (6.02±4.24µg/ml) giving highly significant differences -between them (P=value ≤ 0.000). HbA1c and Homeostasis Model Assessment of Insulin Resistance index (HOMA-IR) differed significantly between the two groups (P-value ≤ 0.000). Serum adiponectin concentrations correlated significantly negative with HOMA IR (r = -0.149, P-value = 0.002). Conclusion: We concluded that low plasma adiponectin level was predictive of future development of Insulin resistance in Sudanese males.

Esterification of free fatty acids in a rotor-stator spinning disc reactor

Esterification of free fatty acids in a rotor-stator spinning disc reactor

Experimental and kinetic study of free fatty acid esterification derived from Ceiba pentandra seed oil with ethanol

Indonesia has an abundant feedstock of Ceiba Pentandra which is very potential as a source for biodiesel production. However, it contains very high free fatty acid and can not be directly converted into biodiesel through transesterification process. One of the solution is by reacting Ceiba pentandra oil with ethanol under acid catalyst called esterification process. In this study, the operating conditions used for esterification reaction was Ceiba pentandra oil to methanol molar ratio of 1:12; with reaction time of 120 minutes. The reaction temperature was varied into 40°C, 50°C, 60°C and 70°C. The results show that, highest conversion achieved was 93.5% at reaction temperature of 70°C. Based on the experimental data, pseudo-Homogeneous model was used to model the kinetic of esterification reaction. Based on this model, the activation energy was 21.319kJ/mol and the kinetic factor was 14,264.08/minutes with R2 of 0.9675 and SSE of 0.0004.

Steady-State and Dynamic Simulation Study of Reactive Distillation for FFA Esterification in Biodiesel Synthesis

Reactive distillation (RD) holds promise for process intensification in biodiesel production since it integrates reaction and separation. It simplifies the process and enhances the conversion of the equilibrium limited reactions. To ensure the stability in RD operation, sensitivity study and process control simulation are necessary. In this work, RD was employed for free fatty acid (FFA) esterification of mixed non edible oils in biodiesel synthesis. Non edible oils used were waste cooking oil, crude jatropha oil, and crude nyamplung oil (Calophyllum inophyllum L). Simulation was conducted using ASPEN Plus V8.8. Sensitivity study was carried out to determine the effects of the operating condition alteration. A dynamic simulation was performed as a Proportional-Integral-Derivative (PID) controller tuning. It was revealed that the highest FFA conversion was 85%, achieved at the feed stage of 7, distillate rate of 0.22 kmol/hr, and oil to methanol molar ratio of 1:5. Level, pressure and temperature controls were installed in RD. Then, a dynamic simulation was applied as a PID controller tuning. Three different controller tuning methods, viz. Ziegler-Nichols, Cohen-Coon, and Internal Model Control, were studied. The best PID parameter was obtained by using Cohen-Coon method which provided fastest rise time, lowest settling time and lowest overshoot.

Ultrasound-assisted enzymatic synthesis of xylitol fatty acid esters in solvent-free conditions

A commercial immobilized lipase was successfully used for the synthesis of five xylityl acyl esters by means of the esterification of free fatty acids (caprylic, capric, lauric and myristic, respectively) with xylitol under solvent-free conditions. Ultrasound-assistance was shown to be a key tool to overcome the handicap imposed by both the mutual immiscibility of fatty acids and xylitol substrates, and the semisolid character of the initial reaction mixtures. In such semisolid systems, ultrasonic irradiation may enable the transport of substrate molecules to the enzyme catalytic-site, leading to the efficient synthesis of xylityl fatty ester (e.g. up to 95% yield after 90 min at 40 °C), with xylityl monoacyl ester and xylitol diacyl ester appearing as the main products (greater than 96%), assessed by HPLC and NMR analyses. The separation of products was carried out by heating and simple centrifugation of the reaction medium, which was possible due to different densities of the resulting fractions.

Polymeric ionic liquids (PILs) with high acid density: Tunable catalytic performance for biodiesel production

A series of polymeric ionic liquids (PILs) used as effective heterogeneous catalysts for biodiesel production via esterification of free fatty acids (FFAs) were effectively prepared by the reaction of poly (ethylene imine) (PEI) polymers with different molecular weight and 1,3-propanesultone, followed by the further acidification with differential effective acids, i.e. H 2 SO 4 , CF 3 SO 3 H, CH 3 SO 3 H or p -toluenesulfonic acid ( p -TSA). Ultrahigh acidity and catalytic performance were achieved and could be fine-tuned by simply adjusting the molecular weight of PEI and by further treatment of acids. Specifically, under the optimal conditions ( i.e. reaction temperature was 70 °C, reaction time was 2.0 h, catalyst dosage was 3.15% (mass), and alcohol/acid molar ratio was 14:1) acquired through the Box-BEHNKEN response surface methodology, a high oleic acid conversion of 98.42% could be obtained over the optimal PIL, PEI(70000)-PS- p -TSA. Additionally, our PILs also showed high generality for esterification of other FFAs, with general high conversion over 90% noted in each case even under much milder reaction conditions compared to other conventional catalysts.