V. Narayana Kalevaru

Defined vanadium phosphorus oxides and their use as highly effective catalysts in ammoxidation of methyl aromatics

The heterogeneous catalytic ammoxidation of methyl aromatics and methyl hetero aromatics is a preferred method for the synthesis of aromatic and hetero aromatic nitriles. The resulting nitriles are valuable intermediates for the production of dyestuffs, pesticides, pharmaceuticals and other chemical products. Usually, the ammoxidation is carried out using V-containing oxides (e.g. V/Ti, V/Sn, V/Mo) promoted by further transition metals as catalysts. However, we have shown recently that defined vanadium phosphates (VPO) revealed an excellent ammoxidation performance. The ammoxidation of toluene was used as model reaction. An intense characterisation of some VPO catalysts under pre-treatment and working conditions by the use of various in situ-methods has thrown more light in formation and stability of the used VPO solids as well as the effect of different reactants (ammonia, toluene) on VPO surface and bulk properties.

Ammoxidation of 2-methylpyrazine to 2-cyanopyrazine over Nb–V oxides: marked effect of the Nb/V ratio on the catalytic performance

A series of bulk Nb–V-containing mixed oxide catalysts with varying Nb/V ratios were synthesized and studied by various solid-state characterization methods. Their catalytic performance was evaluated for the gas phase ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyrazine (CP) that has received growing interest in the chemical industry, recently. The catalysts were characterised by BET-SA, XRD, UV-vis DRS, FTIR, XPS, and TEM. The BET surface area decreased continuously with increase in vanadia content. XRD data confirmed the changes in the crystalline phases with altering Nb/V ratios. UV-vis DRS and FTIR spectroscopic results showed the formation of various kinds of V-oxide species in the catalysts with change in V content. An increase in the concentration of vanadium changes the nature of VOx species from isolated vanadia species to polymeric vanadia species and then to crystalline vanadia species. Among all the catalysts, the Nb–V–O catalyst with a Nb/V ratio of 1 exhibited the best performance in the ammoxidation reaction (i.e. X-MP ~100% and selectivity to 2-CP ~70%). Additionally, a very high space–time yield of CP (>440 gCP kgcat−1 h−1) could be successfully achieved. This best catalyst sample revealed two-dimensional polymeric V-oxide species. TEM and SEM showed the formation of a rod-shaped nanoparticle morphology. XPS data revealed that the vanadium is present in two oxidation states (V5+ and V4+) in the fresh catalyst (Nb/V = 1) and only one oxidation state (V5+) in the spent catalyst.

Metal Nanoparticles as Emerging Green Catalysts

Green nanotechnology is defined as the technology applied for building clean technology by which one can reduce the potential risks of environment and also improve human health conditions. It is linked with the implementation of products of nanotechnology and its process of manufacturing. Green nanotechnology synthesizes new nanoproducts with improved properties in such a way that they can substitute some of the existing low‐quality products. The main motive of developing new nanoproducts is to enhance sustainability and also to make them more environment friendly. In particular, nanoscale materials (e.g., nanoparticles) can be defined as those having characteristic length scale lying within the nanometric range, that is, in the range between one and several hundreds of nanometers. Within this length scale, the properties of matter are sufficiently different from individual atoms/molecules or from bulk materials. The primary objective of this chapter is to provide comprehensive overview about metal nanoparticles (MNPs) and its application as emerging green catalysts. This chapter contains six sections in total. Section 1 starts with a general introduction, recent progress, and brief summary of the application of MNPs as green catalyst. Section 2 reviews the preparation and characterization of supported metal nanoparticles for a wide range of catalytic applications. Section 3 presents the catalytic properties of supported metal nanoparticles. Section 4 describes briefly some of the most commonly reported supported MNPs in different green catalytic applications. Section 5 concentrates on our own results that related to the application of supported MNPs in catalysis. In this section, the oxidation of benzyl alcohol to benzaldehyde, the produc‐ tion of adipic acid from cyclohexane, the photodegradation of dyes using green route will be discussed. Finally, Section 6 describes the summary of main points and also presents an outlook of the application of MNPs in green chemistry.