Archive for the ‘Heterogeneous catalysis’ Category

Nanonets with palladium – good news for green chemistry

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

Porous carbon nanostructures can be excellent catalyst supports, especially for nanoparticles of noble metals such as palladium.

A paper co-authored by Maiyong Zhu and colleagues, in China, describes the use of pre-synthesised α-Fe2O3 nanoparticles as templates to form hollow carbon ‘nanonets’ on which palladium nanostructures are deposited by an in situ precipitation-reduction procedure. The advantage of the hollow nanonet structure is that a higher catalyst loading can be achieved, potentially leading to greater activity towards the target reaction.

Schematic showing formation of palladium catalysts on hollow carbon nanonet supports

The researchers tested their supported palladium catalysts for the Suzuki and Heck  coupling reactions, with good yields although the conversions of substituted substrates tended to be lower than unsubstituted ones. The reactions could also be carried out in water – good news for ‘green’ chemistry.

Compared to supports based on solid carbon spheres, the nanonet supported catalysts had slightly higher palladium loadings and considerably better catalytic performance.

The group have also confirmed through experimental methods that the reactions are indeed catalysed by the supported palladium and not by any leached palladium in solution. The catalysts could be recycled, though there was some loss of activity. Analysis showed that after the Heck reaction, in particular, there was significant aggregation of palladium nanoparticles, thought to be due to temperature effects, as well as deformation of the nanonet carbon structure.

Read more detail about this work in Catalysis Science & Technology:

Hematite nanoparticle-templated hollow carbon nanonets supported palladium nanoparticles: preparation and application as efficient recyclable catalysts
Maiyong Zhu, Ying Wang, Chengjiao Wang, Wei Li and Guowang Diao
Catal. Sci. Technol., 2013, 3, 952-961, DOI: 10.1039/C2CY20562A

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This one is “just right” – Nanoparticle size effects in CO methanation

Posted on behalf of Tien Nguyen, web-writer for Catalysis Science & Technology

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

On May 8th 2013, the NOAA’s (National Oceanic & Atmospheric Administration) Mauna Loa observatory recorded a daily mean concentration of CO2 in excess of 400 ppm, a record high since mankind’s appearance on the planet. As carbon dioxide levels continue to increase at an alarming rate, many laboratories are engaging in alternative energy research to mitigate this problem. 

One such solution involves the methanation reaction, which converts syngas (CO + H2) to synthetic natural gas (CH4). This reaction is highly sought after given that energy from burning natural gas releases approximately 30-45% less carbon dioxide than fossil fuels. 

In this article, researchers evaluated a series of α-Al2O3-supported Ni catalysts of various Ni particle size (5-10, 10-20 and 20-35 nm) for their catalytic efficiency in the methanation reaction. At high temperatures (300-600 °C), ambient pressure and high WHSV (weight hourly space velocity of 240,000 mL/g/h), Ni particles sized 10-20 nm exhibited the highest CO conversion, CH4 yield and turnover frequency, as well as the lowest carbon deposition. 

 

They hypothesized that the smaller Ni particles exhibit more carbon deposition because they have more exposed step edges, which are more susceptible to such formations. They also proposed that Ni particles that are too large may lead to the undesirable growth of carbon nanofibers. Having identified the optimal Ni particle size, the next advancement for the CO methanation reaction lies in improving the stability of these catalysts. 

Read the article here: 

Effect of nickel nanoparticle size in Ni/α-Al2O3 on CO methanation reaction for the production of synthetic natural gas
Jiajian Gao, Chunmiao Jia, Meiju Zhang, Fangna Gu, Guangwen Xua and Fabing Su

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A Green Cocktail for the Industrial Synthesis of Lactic acid

Posted on behalf of Shreesha Bhat

Lactic acid is a versatile chemical having wide applications in food, cosmetics and chemical industry. They are generally prepared by acid catalyzed reactions of hexoses and trioses, and one such triose i.e. glycerol has been found to be produced in surplus amounts as byproducts in production of biodiesel. Glycerol offers great potential to be used as a renewable feedstock for the production of various value-added products like lactic acid.

So far, base catalysts have not been explored for this purpose, except for the hydrothermal conversion of glycerol to lactic acid using alkali metal catalysts like NaOH/KOH. This method presents several drawbacks for the industrial synthesis like harsh reaction conditions (excess temperature, excess amount of strong base, etc.) and cost-intensive isolation of soluble alkali metal lactates (excess catalysts) which is highly uneconomical. As a solution to this problem, scientists at Graz University of Technology, Austria have come up with a “green” method for the industrial synthesis of lactic acid by mixing a cocktail of dihydroxyacetone and calcium hydroxide.

Glycerol to lactic acid

The sparingly soluble calcium hydroxide facilitates the easy removal of excess catalyst by simple mechanical filtration making this a highly economical and industrial friendly method. Another component of the cocktail Dihydroxyacetone– is easily obtained by the microbial oxidation of glycerol in high yields, thus reducing the glycerol burden in the biodiesel industry.

The present paper discusses the catalytic effects of various earth metal hydroxides like barium hydroxide, calcium hydroxide and magnesium hydroxide on the lactic acid formation from dihydroxyacetone. The screening studies indicate that calcium hydroxide is highly selective towards formation of lactic acid owing to its chelation properties. The intriguing mechanism of lactic acid formation by alkali earth metal catalysis was investigated by the means of mechanistic and kinetic studies which suggested two major pathways for lactate synthesis. It was found that the temperature differences play an important role in the preference of the reaction to proceed via either pathway. Various other studies like the effect of concentration of catalyst, feed concentration, temperature variations provide a detailed insight into the synthesis of lactic acid from dihydroxyacetone.

The extensive studies done by the Austrian scientists, has not only provided a potential solution to the enigmatic problem of industrial synthesis of lactic acid, but has also provided a way to recycle the surplus glycerol into a high value product like lactic acid.

To know how the green cocktail made its way to become an industrially feasible method for the synthesis of lactic acid, read the article:

Synthesis of lactic acid from dihydroxyacetone: use of alkaline earth-metal hydroxides
Susanne Lux and Matthäus Siebenhofer
Catal. Sci. Technol., 2013, DOI: 10.1039/c3cy20859a

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Improving conversion efficiency with Ga in solar cells

Adding Ga to CuInS2-based solar cells can improve conversion efficiencyShigeru Ikeda and colleagues from Osaka University, Japan, have evidenced the ease and effectiveness of using spray pyrolysis to make CuInS2-based solar cells in this HOT Catalysis Science & Technology paper.  The effect of Ga-doping on structural properties related to photovoltaic and photoelectrochemical properties were investigated.  Download the manuscript today to find out more…

Fabrication of CuInS2 and Cu(In,Ga)S2 thin films by a facile spray pyrolysis and their photovoltaic and photoelectrochemical properties
Shigeru Ikeda,  Midori Nonogaki,  Wilman Septina,  Gunawan Gunawan,  Takashi Harada and Michio Matsumura
Catal. Sci. Technol., 2013
DOI: 10.1039/C3CY00020F

This article is part of a themed issue on photocatalysis that is due to be published later this year.

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Catalysts losing their nobility

The emission of volatile organic compounds (VOCs) has has been a HOT topic in recent years due to their notorious implication in ozone layer depletion and the formation of ground level ozone.  A specific type of VOC, Polycyclic Aromatic Hydrocarbons (PAHs) are also known to be carcinogenic.  Catalytic oxidation has been utilised as one of the most effective ways to remove unwanted contaminants such as these, however, this usually involves expensive noble metals.  In a move towards alternative materials such as metal-oxides, highly-active CeO2 has recently been applied to reactions such as the above, CO oxidation and soot combustion – however, their widespread uptake by industry has been restricted by their poor thermal stability. 

High thermal stability of ceria-based mixed oxide catalysts supported on zirconia for toluene combustion

Chen et al. have developed a simple, inexpensive and effective solution to the thermal stability problem, by loading mixed CeO2-based oxides on ZrO2.  The catalytic combustion of toluene was studied and the ZrO2 carrier was shown to not only to stabilise the surface active structure of the catalyst but also to improve its efficiency by enhancing O2 mobility.

Read more about the potential of these catalysts by downloading the full article for FREE at:

High thermal stability of ceria-based mixed oxide catalysts supported on ZrO2 for toluene combustion
Han-Feng Lu, Ying Zhou, Wen-Feng Han, Hai-Feng Huang and Yin-Fei Chen
Catal. Sci. Technol., 2013, Advance Article
DOI: 10.1039/C3CY20754D

You may also be interested in a related article:

High activity mesoporous copper doped cerium oxide catalysts for the total oxidation of polyaromatic hydrocarbon pollutants
Asunción Aranda, Elvira Aylón, Benjamín Solsona, Ramón Murillo, Ana María Mastral, David R. Sellick, Said Agouram, Tomás García and Stuart H. Taylor
Chem. Commun., 2012, 48, 4704–4706
DOI: 10.1039/C2CC31206A

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Nano gold boosts the Ullmann reaction

Researchers from the Indian Institute of Chemical Technology have extended the repertoire of C-C bond forming reactions catalysed by gold nanoparticles to include that of the Ullmann reaction.

The Ullmann reaction is an old favourite for synthesising biaryls – it proceeds by coupling together two aryl halides using a transition metal catalyst (traditionally copper).

The heterogeneous catalytic system employed by the authors makes use of gold nanoparticles stabilised on commercially-available nanocrystalline magnesium oxide.

Read more about this work by downloading the article now:

Ullmann coupling of aryl iodides catalyzed by gold nanoparticles stabilized on nanocrystalline magnesium oxide
Keya Layek, H. Maheswaran and M. Lakshmi Kantam

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New trends in the synthesis of crystalline microporous materials

Microporous materials have a wide range of applications, industrially used as catalysts, molecular sieves and ion-exchangers, zeolites are an important class of microporous material that have generated a huge amount of academic and industrial interest in modern times. With over 200 framework types officially recognized by the Structure Commission of the International Zeolite Association, there is also wide diversity in chemical structure and functionality.

This Hot Perspective by Roberto Millini et al. summarises the latest developments in the field of zeolites, with a focus on areas of innovation such as synthetic procedures, framework composition, hybrid materials and morphologies.

This article is free to download, but only for a limited time…………………… As of January 2013 Catalysis Science & Technology is available by subscription only.

New trends in the synthesis of crystalline microporous materials
Giuseppe Bellussi, Angela Carati, Caterina Rizzo and Roberto Millini
Catal. Sci. Technol., 2013, Advance Article
DOI: 10.1039/C2CY20510F

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Making the most of zeolites with graphite oxide

Alexander Todd and Christopher Bielawski from the University of Texas, at Austin have combined zeolites with graphite oxide to enhance their catalytic activities when dehydrating alcohols.

Although both catalysts can be used independently, the team observed a synergistic activity when the catalysts were used in tandem.

Protic zeolites (where H+ is the counter cation) are usually prepared by either ion exchange or high temperature calcination of an ammonium ion exchanged precursor, although ion exchange is not really viable for zeolites with low silica content (such as NaY zeolites). However, Bielawski found that NaY zeolites could be used without either preparation step due to a little help from graphite oxide.

The researchers propose that H+ is released from the graphite oxide upon its dispersion in solvent which exchanges with the Na+ ion in the zeolites to produce the protic form. The graphite oxide–zeolite duo was found to catalyse the dehydration of secondary, tertiary and primary aliphatic alcohols to the corresponding olefinic products with very favourable conversions.

Download the Catalysis Science & Technology article now for more details…

Graphite oxide activated zeolite NaY: applications in alcohol dehydration
Alexander D. Todd and Christopher W. Bielawski

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Sequential synthesis to integrate catalysts – no need to purify

Scientists from Spain have developed a new method for increasing yields in synthetic organic reactions.

One pot syntheses may seem like an attractive option for syntheses with multiple reaction steps but reagents are not always compatible, leading to serious reductions in yields. An alternative sequential approach has been adopted that allows several different heterogeneous catalysts to be used, producing the target compound in much higher yields than the classical approach. Three reactions are conducted in sequence by simply filtering the catalyst after each step and proceeding with the crude mixture.

Sound like a good idea? Read the article for more information…

Integration of Heterogeneous Catalysts into Complex Synthetic Routes: Sequential vs One-Pot Reactions in a (Knoevenagel + Mukaiyama-Michael + Hydrogenation + Transesterification) Sequence
J M Fraile et al, Catal. Sci. Technol., 2012, DOI: 10.1039/c2cy20442h

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Theoretical study of palladium leaching

A collaboration of scientists in China, Germany and Singapore have used a computational model to study palladium leaching processes under a carbon monoxide atmosphere. 

Deactivation of solid catalysts is an important issue in chemical industries and other catalytic applications. One of the causes of deactivation is the loss of active component due to corrosion or leaching by the reaction medium.

The team found that the loss of the active metal component is governed by the structure of the catalyst surface and the pressure (coverage) of carbon monoxide. They concluded that Pd leaching is likely under common catalytic conditions.

To read about the proposed mechanism by which this occurs, read the article now…

Theoretical study on the leaching of palladium in a CO atmosphere
C.-R. Chang et al., Catal. Sci. Technol., 2012

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