Catalysis Science & Technology Blog

Biodiesel can be derived from oil found in animal and plant matter or even from recycled cooking oil. Much research has investigated the catalysis of the esterification and transesterification reactions needed to synthesize biodiesel. In this advance article, Patel and Narkhede contribute a novel catalyst towards the advancement of biodiesel as a competitive renewable energy source.

The authors used mono-lacunary silicotungstate supported on MCM-41, a mobile crystalline material hexagonal silicate, for the acid catalyzed esterification of oleic acid. They optimized the reaction up to 81% conversion with elevated temperature and prolonged reaction times. The researchers demonstrated the heterogenous catalyst could be reused in four iterative reactions without any appreciable loss in activity.

The transesterification of other oils including waste cooking oil, jatropha oil, sunflower oil, cotton seed oil and mustard oil was catalyzed in excellent yields. This catalyst is promising as an environmentally benign component of biodiesel production, though more research needs to be done to decrease the high catalyst loadings.

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Biodiesel synthesis via esterification and transesterification over a new heterogeneous catalyst comprising lacunary silicotungstate and MCM-41
Anjali Patel and Nilesh Narkhede

Tien Nguyen is working towards her PhD in David Nicewicz’s research group at the University of North Carolina at Chapel Hill, USA. Her current area of research focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.

Nitrogen containing aromatic compounds are important in pharmaceutical, materials and agrochemical applications. A direct, catalytic and selective reduction of nitroarenes is a desirable transformation that many groups have targeted.

In this advance article, researchers employed a ceria-supported heterogeneous gold catalyst in combination with 2-propanol as a hydrogen source as a mild system for the selective reduction of nitroarenes. Cao and colleagues obtained excellent yields of azoxyarenes, azoarenes and anilines by varying simple components of the reaction conditions. Running the reduction in the presence of 0.5 equivalents of KOH and water selectively yields the azoarene, while just lowering the amount of water diverts conversion to azoxyarenes. Exclusion of base at elevated temperatures furnishes the primary amine. Though the authors do not know the precise mechanism they propose involvement of a metal-hydride species similar to the Haber electrochemical hydrogenation.

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Mild, selective and switchable transfer reduction of nitroarenes catalyzed by supported gold nanoparticles
Xiang Liu, Sen Ye, Hai-Qian Li, Yong-Mei Liu, Yong Cao and Kang-Nian Fan
Catal. Sci. Technol., 2013, Advance Article

Tien Nguyen is working towards her PhD in David Nicewicz’s research group at the University of North Carolina at Chapel Hill, USA. Her current area of research focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.

Synthetic chemists have long been attempting to attain the exquisite levels of substrate selectivity offered by enzymes. Heterogeneous catalysts can provide high selectivities through the control of their porosity. While there are some strategies for achieving selectivity with homogeneous catalysis, this field still lags behind its enzymatic and heterogeneous counterparts.

In this advance article, Strukul and co-workers demonstrated substrate selectivity in the hydration of alkynes using a NHC-Au(I) catalyst encapsulated in a hexameric resorcin host. In the presence of the encapsulated catalyst the cyclic aliphatic alkyne was converted to product faster than the longer chain linear substrates. The authors ascribe this effect to the better fit of the cyclic substrate into the host cavity. Aromatic substrates were also tested and showed low yields likely due to their increased rigidity. Overall, aliphatic and aromatic alkynes were hydrated in low to modest yields but the observed trends serve as a valuable proof of concept.

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Substrate selectivity in the alkyne hydration mediated by NHC-Au(I) controlled by encapsulation of the catalyst within a hydrogen bonded hexameric host
Alessandra Cavarzan, Joost N. H. Reek, Francesco Trentin, Alessandro Scarso, and Giorgio Strukul
Catal. Sci. Technol. 2013, Advance Article, DOI: 10.1039/c3cy00300k

Tien Nguyen is working towards her PhD in David Nicewicz’s research group at the University of North Carolina at Chapel Hill, USA. Her current area of research focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.

A study published in the journal Diabetes Care estimated that in 2000, 171 million people worldwide had diabetes. People with diabetes have high blood sugar levels so biosensors that detect glucose are crucial in the diagnosis and treatment of this disease. Many diagnostic glucose sensors have been developed with widespread use in clinical and biotechnology applications.

In this Catalysis Science & Technology advance article, Liu and co-workers developed a colorimetric method for the detection of H₂O₂. Hydrogen peroxide is a by-product formed when glucose is oxidized by glucose oxidase (GOx), so coupling these events is a common strategy for glucose detection. The resultant H₂O₂ in the presence of an oxidation catalyst oxidizes 3,3,5,5-tetramethylbenzidine (TMB) to the diimine (oxTMB) producing a deep blue color. The researchers synthesized a composite material (H@M)to catalyse the oxidation by anchoring Hemin, to an amino-containing MOF (MIL-101(Al)-NH₂).

This represents the first use of a MOF-artificial enzyme in glucose detection. Immobilizing Hemin on a metal-organic framework prevents problematic oxidative degradation and molecular aggregation. Also, the pore structure of the MOF mimics protein structure, which is important for activity and selectivity. The catalytic activity of this enzyme mimic is dependent on pH, temperature and H₂O₂ concentration. However, glucose oxidation is optimal at a pH of 7.0 and TMB oxidation by H@M is optimal at a pH of 5.0. The glucose detection is finally realized by first reacting glucose with GOx then adding a TMB and H@M solution and adjusting the acidity of the solution.

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Hemin@metal-organic framework with peroxidase-like activity and its application to glucose detection

Feng-Xiang Qin, Shao-Yi Jia, Fei-Fei Wang, Song-Hai Wu, Jia Song and Yong Liu

Catal. Sci. Technol. 2013, Advance Article, DOI: 10.1039/c3cy00268c

Tien Nguyen is a web contributor working towards her PhD in David Nicewicz’s research  group at the University of North Carolina at Chapel Hill, USA. Her current area of research  focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.

Hydrogenated acrylonitrile butadiene rubber (HNBR) is an important elastomer heavily relied on by the automotive and petroleum industry. Identified for its tensile strength and ability to resist oxidative degradation, HNBR is used to make seals, hoses and belts. On an industrial scale, HNBR is synthesized by the hydrogenation of unsaturated acrylonitrile butadiene rubber (NBR). This process involves an organic solvent, hydrogen gas and a transition metal catalyst.

In this advance article, Rempel, Pan and co-workers have developed a green method to hydrogenate NBR that employs water-soluble Rhodium catalysts in purely aqueous media. Rhodium chloride monosulfonated triphenylphosphine (RhCl(TPPMS)₃, 0.52 mmol L^-1) catalysed the hydrogenation of NBR (50 g L^-1) with a 95% conversion to HNBR in 9 hours at 1000 psi and 100 °C. The solubility of the Rhodium catalyst was critical to the success of the reaction, creating an effective relative partition between the water and polymer phases.  The authors also found that NBR starting materials containing gel resulted in lower conversions because this structure limits contact between the active catalyst and substrate.

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Hydrogenation of acrylonitrile-butadiene copolymer latex using water-soluble rhodium catalysts

Yin Liu, Hanmiroo Kim, Qinmin Pan, and Garry L. Rempel

Catal. Sci. Technol., 2013, Advance Article, DOI: 10.1039/c3cy00257h

Tien Nguyen is a web contributor working towards her PhD in David Nicewicz’s research  group at the University of North Carolina at Chapel Hill, USA. Her current area of research  focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.

The majority of laboratory scale organic reactions rely on homogenous catalysts which are usually removed via chromatography, often a time-consuming process that generates solvent and silica gel waste. These separation issues become untenable for large scale industrial processes and as a result, heterogeneous catalysts are preferred for ease of isolation. To be adopted as an industrial process, the reaction must also satisfy high standards of conversion to product, costliness and enantioselectivity.

This article details the asymmetric epoxidation of alkenes using heterogeneous iminium micro- and mesoporous supported organocatalysts with TPPP (tetraphenylphoshonium monopersulfate) as a stoichiometric oxidant. This method holds potential for industrial production as the catalyst can be reused after simple filtration and washing and avoids the use of expensive transition metals. Enantiopure epoxides, which are valuable synthetic building blocks, were obtained in high yields and enantioselectivities for select alkenes. Successive uses of the catalyst do however result in lower yields for reasons currently unknown to the authors. Nonetheless this report may serve as valuable precedent for future efforts towards a reusable heterogeneous chiral iminium catalyst for epoxidation.

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Towards heterogeneous organocatalysis: chiral iminium cations supported on porous materials for enantioselective alkene epoxidation
Philip C. Bulman Page, Andrew Mace,  Damien Arquier, Donald Bethell, Benjamin R. Buckley, David J. Willock, and Graham J. Hutchings
Catal. Sci.Technol., 2013, DOI: 10.1039/c3cy00352c

Tien Nguyen is a web contributor working towards her PhD in David Nicewicz’s research  group at the University of North Carolina at Chapel Hill, USA. Her current area of research  focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.

According to the USDA foreign agriculture service, the European Union consumed 13.8 billion litres of biodiesel in 2012. The increasing demand for biodiesel stems from its lower greenhouse gas emissions, estimated to be 57% lower than emissions from burning petroleum diesel.  To become competitive with fossil fuels, alternative energy sources must achieve low production costs starting from abundant feedstocks.

In this Advance Article, Yang and co-workers reports the transesterification of several oils to biodiesel (primarily fatty acid methyl ester, FAME), obtaining >97% yields using 3 wt% calcined porous calcite or dolomite catalysts. Prepared through simple thermal decomposition of cheap Mg/Ca carbonate minerals and stearic acid mixtures, these heterogeneous catalysts possess high special surface areas (SSAs) increasing the sites accessible for reactivity.

The researchers found that the catalysts could be regenerated by treatment with stearic acid, and re-used with no appreciable loss in activity. The authors propose that this process could be well-suited for industrial application as it is inexpensive and environmentally benign.

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A facile, low-cost route for the preparation of calcined porous calcite and dolomite and their application as heterogeneous catalysts in biodiesel production

Rui Wang. Hu Li, Fei Chang, Jiafeng Luo, Milford A. Hanna, Daoyang Tan, Deyu Hu, Yuping Zhang, Baoan Song, and Song Yang

Catal. Sci. Technol., 2013, DOI:10.1039/C3CY00129F

Tien Nguyen is a web contributor working towards her PhD in David Nicewicz’s research  group at the University of North Carolina at Chapel Hill, USA. Her current area of research  focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.