Design And Development Of Novel Nanocatalysts;A Key Tool Towards Sustainability

This thesis constitutes upon three parts;in the first part,we report the very first example of gadolinium hydroxide(Gd(OH)3)nanorods as support for loading ultra-small Pd nanoparticles for hydrogenation reactions.Gd(OH)3 possesses a large number of hydroxyl groups on the surface which act as an ideal support for well dispersion of Pd nanoparticles.Gd(OH)3 nanorods are prepared by hydrothermal treatment,and surface-clear Pd/Gd(OH)3 catalyst with a low loading of 0.95 wt%Pd is obtained by photochemical deposition.The catalytic hydrogenation of p-nitrophenol(4-NP)to?-aminophenol(4-AP)and styrene to ethylbenzene is performed as model reaction,the obtained Pd/Gd(OH)3 catalyst displays highly excellent activities as compared to other reported heterogeneous catalysts.The rate constant of 4-NP reduction is measured to be 0.047 s-1 and Pd/Gd(OH)3 nanocatalyst shows no marked loss of activity even after 10 consecutive cycles.Additionally,the hydrogenation of styrene to ethylbenzene over Pd/Gd(OH)3 nanorods exhibits turnover frequency(TOF)as high as 6159 h-1 with 100%selectivity.Moreover,the catalyst can be recovered by centrifugation and recycled up to 5 consecutive cycles without obvious loss of activity.Our results indicate that Gd(OH)3 nanorods act as promoter to enhance the catalytic activities by providing synergistic effect from strong metal support interaction and large surface area for high dispersion of small sized Pd nanoparticles with clean surfaces.The high performance of Pd/Gd(OH)3 in heterogeneous catalysis offers a new,efficient and facile strategy to explore other metal hydroxides or oxides as support for organic transformations.In the second part;we demonstrate a novel metal-acid bifunctional nanocomposite of finely scattered metallic Ru nanoclusters(NCs)sustained on porous hafnium phosphate nanoplates(?-HfP NPs)to effectively depolymerise lignocellulosic biomass.A native lignin fraction of pine lignocellulose was promptly depolymerised into 19.86 wt%yield(lignin based)of valuable phenolic monomers(with dihydroeugenol as the main compound in high selectivity)and few cyclic ketones through one-pot catalytic reductive fractionation under mild conditions(190 ?,3.5 MPa H2).Detailed scanning and transmission electron microscopy,X-ray photoelectron spectroscopy,and temperature-programmed desorption ammonia investigation correlated with the obtained results revealed that the metal-acid synergistic influence and presence of Brensted acid site in support for dehydration and the well-dispersed metallic role of Ru NCs for hydrodeoxygenation were responsible for the cleavage of lignin-carbohydrate(ester and ether linkages)bonds.Moreover,treating commercial lignin as a substrate in an organic solvent generated 4-hydroxy-3-methoxybenzaldehyde(vanillin)in high yield,as well as other functionalised phenolic monomers up to 85%selectivity,illustrating the high susceptibility of Ru/a-HfP NPs towards C-O bond cleavage through reductive fractionation.Multiple recycling tests of catalyst were performed without apparent loss of activity.Overall,this report highlighted the potential of synthesis strategy of metal—acid supported catalyst to immediately depolymerise untreated biomass and can thus encourage the green,cost-efficient,large-scale production of intermediate chemicals.In the last and third part;we described a facile,sustainable,and economical one-pot solvothermal method to produce Co-MOF nanosheets,using 4,4'5,5'-tetracarboxyl-2,2'-biimidazole(denoted as H6tcbi)as organic linker The size,shape and structural morphology of as-synthesized Co-MOF nanosheets were systematically characterized by means of SEM,TEM,XRD,XPS,and FT-IR scientific methods.N2 adsorption-desorption and CO2 adsorption analysis identifies the porosity nature and adsorption properties of Co-MOF nanosheets.Moreover,as-synthesized Co-MOF as heterogeneous catalyst displays a remarkable capability towards C02 capture and conversion into commercially valued cyclic carbonates with high yield(-97%)in solvent-free atmosphere under relatively mild reaction conditions(5 bar,80 ?,3 h).Notably,the Co-MOF catalyst could be successfully recycled up to numerous turns without an obvious loss of catalytic activity and structural deformation,which are the most critical constraint for 2D MOF complexes in industrial scale viability.