Catalysis Science & Technology Blog

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

Amin Osatiashtiani,   D Robert Brown,   Adam F Lee,  Gabriel Morales,   Juan Antonio Melero and   Karen Wilson

Catal. Sci. Technol., 2013, Accepted Manuscript

DOI: 10.1039/C3CY00409K

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.

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.

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.

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 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.

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