Archive for the ‘Heterogeneous catalysis’ Category

Poison or not poison… Another side to sulfur

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


Sulfur is normally thought of as a catalyst poison – but a Perspective article in Catalysis Science and Technology, by Alan McCue and  James Anderson at the University of Aberdeen, UK, reports on a growing quantity of work suggesting that it can act as an activity promoter or selectivity modifier in heterogeneous catalysis.

Catalytic metals including rhodium, platinum and palladium are well known for being susceptible to sulfur as a poison, however the effect is perhaps not as simple as first perceived – it has been suggested that the effects of sulfur have a degree of long range character, indicating that a small quantity of adsorbed sulfur may have a disproportionate effect on catalytic properties.

Many industrial feedstockSchematic representation of how relative activity varies with approximate wt% sulfur per unit mass catalysts and even biomass derived feedstocks contain sulfur to some extent which may influence catalytic performance. With more than 100 references, this article may provide a useful source of further information on this very relevant topic.

The authors present examples from Fischer–Tropsch synthesis, catalytic reforming, regio- and chemoselective hydrogenation as well as CO oxidation, hydrocarbon oxidation and NOx reduction.

Find out more by reading the article:
Sulfur as a catalyst promoter or selectivity modifier in heterogeneous catalysis

Catal. Sci. Technol., 2014, DOI: 10.1039/C3CY00754E

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All that glitters – gold and palladium serve catalysis needs

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


Gold-palladium nanoparticles are hot stuff when it comes to catalysis. Catalysis Science and Technology’s themed issue, entitled ‘Gold Catalysis’, highlights just three examples of the many studies that regularly appear in the literature.

A minireview from Pasi Paalanen et al., Utrecht University, gives an overview of recent developments in the synthesis of supported gold-based bimetallic nanoparticles for catalytic applications. They focus on three major structural features to be characterised and, where possible, controlled: size, composition and nanostructure. They highlight selected literature examples in which gold-palladium nanoparticles were found to be active for reactions such as CO oxidation, vinyl acetate synthesis, cyclotrimerization of acetylene to benzene, selective oxidation of alcohols to aldehydes or ketones, direct synthesis of hydrogen peroxide, hydrocarbon hydrogenation, oxidation of primary C–H bonds, hydrodechlorination and hydrodesulfurization.

chloronitrobenzene hydrogenation and hydrogen peroxide synthesis over gold palladium nanoparticlesMeanwhile Elena Corbos and her colleagues at Johnson Matthey Technology Centre, in collaboration with Synchrotron Soleil, France, and University College London, present some original research on the preparation of bimetallic PdAu nanocatalysts. They tested the catalysts for the selective hydrogenation of 2-chloronitrobenzene to 2-chloroaniline and the direct formation of hydrogen peroxide. They found that a Pd-rich surface offered superior selectivity and reaction rates for 2-chloronitrobenzene hydrogenation, while for hydrogen peroxide synthesis, an optimal quantity of gold was required to ensure high productivity.

Tatsumi Ishihara et al., Kyushu University, Japan, carried out synthesis of hydrogen peroxide by direct oxidation of hydrogen in air on gold-palladium/titania. They report that the H2 conversion and H2O2 selectivity were strongly affected by the crystal phase of the titania. With increasing H2 pressure, H2O2 selectivity increased on AuPd/rutile TiO2 and the yield of became higher than on brookite or anatase TiO2 at 1.0 MPa. The effects of fluorinated hydrocarbon addition to reaction media were also studied.

Find out more about all this research in Catalysis Science and Technology.

Progress in controlling the size, composition and nanostructure of supported gold–palladium nanoparticles for catalytic applications
Pasi Paalanen, Bert M. Weckhuysen and Meenakshisundaram Sankar
Catal. Sci. Technol., 2013,3, 2869-2880, DOI: 10.1039/C3CY00341H

Tuning the properties of PdAu bimetallic nanocatalysts for selective hydrogenation reactions
Elena C. Corbos, Peter R. Ellis, James Cookson, Valérie Briois, Timothy I. Hyde, Gopinathan Sankar and Peter T. Bishop
Catal. Sci. Technol., 2013,3, 2934-2943, DOI: 10.1039/C3CY00255A

Effects of fluorinated hydrocarbon addition on H2O2 direct synthesis from H2 and air over an Au–Pd bimetallic catalyst supported on rutile-TiO2
Tatsumi Ishihara, Kohei Shigeta, Yuuki Ooishi, Maki Matsuka, Hidehisa Hagiwara and Shintaro Ida
Catal. Sci. Technol., 2013,3, 2971-2975, DOI: 10.1039/C3CY00273J

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Chemical Cross-linking of lipase in Mesoporous silica: A new addition to the enzyme immobilization kit

themed issue on Enzyme Immobilization was recently published in Chemical Society Reviews encompassing the advances made in the field of enzyme immobilization and its importance in the Industrial arena. The credit goes to a simple discovery by Nelson and Griffin, who in 1916 rediscovered that artificial carrier-bound invertase on Al(OH)3 and charcoal was still catalytically active. They put to rest the claims that substances like charcoal caused inhibition of the enzymes (due to adsorption) and established that adsorption had no role in the decreased activity of the enzymes. This discovery laid the foundation for the immobilized enzymes to find wide applications in the chemical industry.

The carriers used for immobilization include natural and synthetic polymers like cellulose, starch,  polystyrene, sephadex and inorganic carriers like clay, kaolinite, silica gel etc. Of these, Mesoporous silica materials (MPS) have been found to be an attractive alternative due to their intrinsic properties. The immobilization of the enzymes on these carriers are generally carried out by physical adsorption or covalent binding, but face the problem of enzyme leaching. In order to overcome this problem, the Cross-linked enzyme aggregates (CLEAs) method has emerged of late and has been successful to a certain extent. In the present paper, the authors have explored the CLEAs of lipase from Candida sp. 99-125 immobilized in MPS and found them to be thermally and catalytically stable with  improved enzymatic activities.

As a measure of their improved properties, the activity and stability of the Cross-linked lipases in MPS (nicknamed CLL@MPA) were compared with the simple adsorbed lipases (ADL@MPA) and the native enzymes, and were found to be highly stable (at high temperatures as well as on shaking) with improved hydrolytic, esterification and transesterification activites. Although these lipases (from candida sp. 99-125) were less active than the commercially available Novzyme 435 (from candida antarctica), their cheaper costs make them a promising alternative for industrial applications.

This study thus paves the way for cheaper and effective enzyme immobilization options, which can be further extended to other enzymes and lead to potential advances in various enzyme-based industrial processes.

Lipase Candida sp. 99-125 CLEAs in MPS

Lipase CLEAs in mesoporous silica- a robust biocatalyst with increased stability and recyclability

Read more at:

Formation of lipase Candida sp. 99-125 CLEAs in mesoporous silica: characterization and catalytic properties
Jing Gao
,   Lianlian Shi,   Yanjun Jiang,   Liya Zhou and   Ying He
Catal. Sci. Technol.
, 2013, Accepted Manuscript
DOI:
10.1039/C3CY00412K


Shreesha Bhat, Web Writer Shreesha Bhat is a M.S.(Pharm.) in Medicinal Chemistry from National Institute  of  Pharmaceutical  Education and Research,  India. His area of interests  include  chemical  synthesis of biologically important  molecules  and developing  newer    methods for organic  synthesis using novel catalysts.

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Art in action: Novel Sulfated Zirconia as bifunctional catalysts

With context to the ever increasing problem of dwindling energy resources, sugars like 5-Hydroxymethylfurfural (5-HMF) and furfural are considered to be the key for next-generation energy demands. These sugars have been recently identified to have potential applications in the petrochemicals and plastic industry. While efforts are ongoing to find a cheaper and greener way for the production of 5-HMF, it has eluded most of the researchers till now.

In their quest for a total green 5-HMF synthesis, the authors moved towards sulfated zirconia as a bifunctional catalyst for the one-pot conversion of glucose to 5-HMF in aqueous phase. It has been observed that isomerisation of glucose to fructose is possible with zirconia, and the subsequent dehydration of fructose to 5-HMF with sulfated zirconia (SZ). The authors tried to capitalize on their previous experience of employing SZ in aqueous media and went on to create the first ever bifunctional catalyst for 5-HMF production in water. The key towards the holy grail was tuning the acid strength in SO2/ZrO2 to achieve both the isomerisation and dehydration through a single bi-functional catalyst.

Sulfated Zirconia as bifunctional catalysts

The amphoteric nature of  zirconia was explored and tuned by adjusting the sulfate loading onto the metal, as the surface sulfate density directly relates to the acidity of the catalyst. The extensive investigations by the researchers showed that zirconia exists in a monoclinic state with large lewis base sites, which converts to a more stable tetragonal structure on sulfate addition with abundance of bronsted acid sites. The lewis base sites catalysed the glucose –> fructose isomerisation and the bronsted acid sites accelerated the fructose –> 5-HMF dehydration. This knowledge helped them in optimising the sulfate loading to 0.3 ml which gives a perfect platform for Glucose –> Fructose –> 5-HMF conversion.

To read more about the art of synthesizing such novel bifunctional catalysts, follow the link below:

Bifunctional SO4/ZrO2 catalysts for 5-hydroxymethylfurfural (5-HMF) production from glucose

Catal. Sci. Technol., 2013, Accepted Manuscript
Shreesha Bhat, Web Writer Shreesha Bhat is a M.S.(Pharm.) in Medicinal Chemistry from National Institute  of Pharmaceutical        Education and Research, India. His area of interests  include chemical synthesis of biologically important  molecules and developing  newer methods for organic synthesis using novel catalysts.
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Pd Nanocubes: A new customizable weapon for enantioselective hydrogenation

Ever heard of a customizable catalyst? A catalyst with a unique shape? A catalyst which with a change in size can provide different activity? If not, then here is a catalyst- an easy to prepare Pd nanocube which you can customize as per the activity desired: racemic or enantioselective hydrogenation of α,β-unsaturated carboxylic acids.

The enantioselective hydrogenation of aliphatic α,β-unsaturated carboxylic acids faces the obstacle of lower enantioselectivities as the aliphatic substituent is not armed to curb the inevitable isomerization of the double bonds in the structure. High enantioselectivities have been observed in cases of aryl substituted α,β-unsaturated carboxylic acids owing to the stabilizing effect of the aryl substituent at the β-position. With no effective solutions up-to-date, the researchers at Chinese Academy of Sciences tried to find the answer to this problem in the world of micromeretics and morphology.

Considering the previous instances where the sizes and shape of the catalysts did play a role in the enantioselectivity, the researchers tried to capitalize on this and were indeed rewarded with fruitful results. They decided to study the effects of shape and size, by preparing both cubic and spherical Pd nanoparticles as catalysts for the enantioselective hydrogenation of unsaturated carboxylic acids. The studies conducted by the Shen group clearly indicate that the Pd nanocubes have a upperhand, as they provide good enantioselectivities as compared to the spherical nanoparticles. They also found that the Pd nanocubes of larger size provided with excellent enantioselecctivities as compared to the smaller nanocubes. The dynamics of this can be explained by the fact that larger nanocubes, which have more flat sites, can easily accommodate the chiral modifier (like cinchonidine) on its surface along with the substrate, thus resulting in higher enantioselectivities. Meanwhile, the smaller nanocubes provided higher yields, as they are equipped with more edge sites, which accelerates the process of hydrogenation. The present study provides with a customizable formula with both small and large nanocubes put to different use.

Activity desired Pd Nanocubes customized to
Racemic Hydrogenation at High yields Small  size
Enantioselective Hydrogenation at Lower yields Large size

Thus, the present paper brings forward the fresh concept of customized Pd nanocubes, which can be an effective weapon in the armory of catalysts for enantioselective hydrogenation of α,β-unsaturated carboxylic acids.

Palladium nanocubes as customizable weapons for enantioselective hydrogenation

Customizable Palladium Nanocubes for Racemic/Enantioselective hydrogenation

To read more, follow the link below:

Enantioselective hydrogenation of α,β-unsaturated carboxylic acids on Pd nanocubes
Chunhui Chen, Ensheng Zhan, Na Ta, Yong Li and  Wenjie Shen

Catal. Sci. Technol., 2013, Advance Article
DOI:
10.1039/C3CY00314K

Shreesha Bhat, Web Writer Shreesha Bhat is a M.S.(Pharm.) in Medicinal Chemistry from National Institute of Pharmaceutical        Education and Research, India. His area of interests include chemical synthesis of biologically important  molecules and developing newer methods for organic synthesis using novel catalysts.

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Turn up the heat – Thermal treatment key to magnetically recoverable AuPd nanoparticles

Aldehydes are valuable synthetic intermediates with many methods for their preparation. But the majority of these approaches employ stoichiometric oxidants that produce toxic waste. Aerobic oxidation with molecular oxygen and a transition metal catalyst offers an environmentally benign alternative. In this advance article, Rossi and colleagues reported the first magnetically recoverable AuPd nanoparticle catalyst applied to the oxidation of primary alcohols to aldehydes.

The removal of metal catalysts supported on magnetic surfaces with an external magnetic field is an innovative and efficient method for separation.  The researchers achieved linkage by dually functionalizing the support with strongly coordinating ligands and impregnating the nanoparticles with weak coordinating groups in the coordination capture method. They found that catalysts with amino-functionalized silica supports exhibited higher activity and stability to catalyst recycling than the analogous thiol supports. The authors achieved a 92% conversion of benzyl alcohol with high selectivity for benzaldehyde using 1 wt% AuPd catalyst (Fe3O4@SiO2-NH2-AuPd) under 6 bar of O2 at 100 °C. However, catalyst separation was impeded by the amino group, which had reacted with the product benzaldehyde to form an aldimine.

This issue was circumvented through the calcination of the Fe3O4@SiO2-NH2-AuPd catalyst at 500 °C for 2 hours, effectively removing the amino groups and promoting highly efficient catalyst recovery. Good yield and selectivity for the oxidation reaction was maintained and the catalyst was used in five successive reactions without loss of selectivity.

To read more, follow the link below:

Magnetically recoverable AuPd nanoparticles prepared by a coordination capture method as a reusable catalyst for green oxidation of benzyl alcohol

Tiago A. G. Silva, Richard Landers and Liane M. Rossi

Catal. Sci. Technol., 2013, Advance Article, DOI: 10.1039/c3cy00261f

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

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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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