Catalysis Science & Technology Blog

Posted on behalf of Shreesha Bhat

The trend of employing metal alloys as catalysts in various organic reactions is gaining popularity owing to the considerable advantages it offers. Alloying gold with palladium is known to enhance the activity of the formed catalyst for various oxidation reactions. Present methods employed for the preparation of Au-Pd alloys include wet impregnation, deposition precipitation and sol-immobilization. These methods utilize chloride salts of the gold as a precursor which make the removal of the chloride from the final catalyst difficult. The presence of chloride is known to cause a loss in the catalytic activity of the alloys through blocking of the active sites. Scientists have been trying to find a way to reduce the chlorine content, but the alternatives have been equally discouraging due to various problems associated with them.

In an answer to this challenging problem, Researchers from UK and Pakistan have come up with a simple solution: Simply grind the metal acetates for 10 min with a support and get highly active chloride-free alloys as oxidation catalysts. These catalysts were evaluated against catalysts prepared by impregnation for the oxidation of benzyl alcohol, glycerol and direct H₂O₂ synthesis.

Various optimization studies on the Au:Pd ratio and the metal loading were carried out using turn over frequency (TOF) as the standard for comparisons. The results indicated that the physical grinding (PG) facilitated the Pd-Au alloy formation (not observed with other methods) which is known to produce a synergistic effect on the catalytic activity. It was also found that an optimum ratio of both metals resulted in higher activity with optimum metal loadings. To provide the icing on the cake, the PG (physically ground) catalysts were further successfully employed for the oxidation of various substrates with equal (or improved) TOFs, thus proving the general applicability of these catalysts.

Thus, the present paper showcases how the conventional physical grinding was successful in providing highly active bimetallic catalysts, where most of the other complex methods faltered!!

To read more, follow the link below:

Physical mixing of metal acetates: optimisation of catalyst parameters to produce highly active bimetallic catalysts
Peter J. Miedziak, Simon A. Kondrat, Noreen Sajjad, Gavin M. King, Mark Douthwaite, Greg Shaw, Gemma L. Brett, Jennifer K. Edwards, David J. Morgan, Ghulam Hussain and Graham J. Hutchings
Catal. Sci. Technol., 2013, Advance Article
DOI: 10.1039/C3CY00263B, Paper

Shreesha Bhat is a medicinal chemist pursuing his M.S.(Pharm.) in Medicinal Chemistry at the National Institute of Pharmaceutical Education and Research, India

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.

Read the full article here:

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.

Read the full article here:

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.

Posted on behalf of Tien Nguyen 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.

To satisfy the energy demands of an ever-increasing population, it is critical to develop renewable energy sources. Photocatalytic hydrogen production from water stands out among the alternatives as this process yields a clean energy source and relies on visible light, which has exciting implications for harnessing the power of the sun.

In this article, Matsuoka and co-workers report efficient hydrogen production employing a Pt-deposited amino-functionalized Ti metal organic framework catalyst (Pt/Ti-MOF-NH₂) in aqueous triethanolamine (TEOA) and visible light. The organic linker serves to absorb the light and donate electrons to the titanium-oxo cluster with TEOA present as a sacrificial electron donor. An optimal loading of 1.5 wt% was found for the Pt cocatalyst, which is proposed to trap the photogenerated electrons and suppress unproductive electron-hole recombination.

The authors also successfully extended this system to the reduction of nitrobenzene, providing an environmentally benign alternative to existing methods. They found that the photocatalyst could be reused at least three times with no appreciable loss in activity. These findings hold promise for the development of highly efficient photocatalysts promoted by naturally abundant sunlight.

Read the full article here:

Efficient hydrogen production and photocatalytic reduction of nitrobenzene over a visible-light-responsive metal–organic framework photocatalyst
Takashi Toyao, Masakazu Saito, Yu Horiuchi, Katsunori Mochizuki, Masatoshi Iwata, Hideyuki Higashimura and Masaya Matsuoka

Catal. Sci. Technol., 2013, DOI: 10.1039/c3cy00211j

Sara Coles is a guest web-writer for Catalysis Science & Technology. She
currently works for Johnson Matthey in Royston, UK.

Foam, fleece and honeycomb have one unexpected thing in common: they are all physical structures that can be made into supports for industrial platinum catalysts.

Patrick Sonström and colleagues in Germany have studied the deposition of colloidally preformed nanoparticles of platinum deposited with or without a washcoat onto low surface area codierite honeycombs, alumina foam and nickel fleece.

Their technique allows higher platinum loadings to be applied without the disadvantages of agglomeration and adhesion, meaning that higher catalytic activities can be achieved on low surface area substrates.

This could have potential to expand the use of monolithically supported platinum catalysts beyond their automotive niche and into wider industrial use for reactions such as methanol steam reforming, oxidative dehydrogenation of propane and liquid phase hydrogenations. The advantages of monolithic catalysts over their classic pellet bed alternatives include lower pressure drops and improved mass transfer.

To find out more about this work read the article in Catalysis Science & Technology:

Foam, fleece and honeycomb: catalytically active coatings from colloidally prepared nanoparticles
Patrick Sonström, Birte Halbach, Sonia Tambou Djakpou, Beate Ritz, Kirsten Ahrenstorf, Georg Grathwohl, Horst Weller and Marcus Bäumer

Catal. Sci. Technol., 2011, 1, 830–838, DOI: 10.1039/c1cy00077b