Over the past decades, since the discovery of a single–site silica-supported catalyst for the alkane metathesis reaction by our group, we have been extensively working on the development of supported catalytic systems for the improved alkane metathesis reaction. During these developments, we understand the reaction mechanism and reached a new perspective for the synthesis of various supported bimetallic systems via the surface organometallic chemistry (SOMC) approach. Recently, with this bi-metallic system, we got a very high TON (10000) in propane metathesis reaction. As these catalysts are very efficient for linear alkanes we thought to apply it for cyclo-alkanes specifically, for cyclo-octane metathesis expecting better activity. Besides, the value of the ring alkanes are higher than the linear alkanes. The current work demonstrates a combination of [(ΞSi−O−)W(Me)5] and [(ΞSi− O−)Ti(Np)3 pre-catalyst with several supports (SiO2-700, SBA-15 and MCM-41) for metathesis of cyclooctane. The catalysts have been synthesized and fully characterized by elemental analysis (EA), FT-IR and NMR spectroscopies. After fully characterization the bi-metallic catalyst was tested for metathesis of cyclooctane with highest ever TON 2500 as compared to that of mono-metallic catalyst where we got 430 TON. Which again corroborates our prediction that bimetallic catalysts are better catalysts than monometallic catalysts.

No description available.

Self-propagating High-temperature Synthesis (SHS) is the synthesis of solid materials by a reaction wave propagating into the initial reactants, typically two metals, which can alloy exothermically. Typically, experiments are performed with the reactants in powder form, with relatively low density. Recent experiments by Bacciochini et al. revealed much larger flame speeds in densified powders near TMD (theoritical maximum density), obtained by the cold spray process. The present thesis investigates why the flame speed increases dramatically with an increase in density of the powders. The investigation rests on the analytical model formulated by Makino by controlling how the variables are affected by changes in density. Flame speed measurements were performed in mixtures of nickel (Ni) and aluminum (Al) at different initial densities. The density was varied by controlling the cold-pressing of the samples inside metallic channels and tubes. Experiments were also performed in ball-milled powders, in order to permit comparison with the experiments performed by Bacciochini in these mixtures at nearly maximum densities. The measurements revealed that the flame speed increases with the initial density, with a discontinuous transition occurring at approximately 60% theoretical maximum density (TMD). This transition also corresponds to the point where the powders deform plastically during the compaction process, suggesting that the intimate contact between the particles is responsible for the flame speed increase. The flame speed dependence on powder density is attributed to the changes in the heat conductivity of the pressed powders. At high densities, where the powders have plastically deformed, the continuous structure yields conductivities close to the idealized solid matrix. At these high densities, the conductivity was modeled using the Effective Medium Theory (EMT). Analytical predictions of the flame speed, using available thermo-chemical data for the Al-Ni system were found in good agreement with the present experiments at high densities. At low densities, since Al-Ni is a mixture of loose powders, the EMT model is no longer applicable. Thus, the thermal conductivity was experimentally measured and then was fitted using the semi-empirical model suggested by Aivazov. Using this data, Makino's model predicts the correct flame speed dependence observed experimentally. The present thesis has thus established that the dependence of flame speed on density is due mainly to the changes in the structure and thermal conductivity of the powders.

No description available.

Self-propagating High-temperature Synthesis (SHS) is the synthesis of solid materials by a reaction wave propagating into the initial reactants, typically two metals, which can alloy exothermically. Typically, experiments are performed with the reactants in powder form, with relatively low density. Recent experiments by Bacciochini et al. revealed much larger flame speeds in densified powders near TMD (theoritical maximum density), obtained by the cold spray process. The present thesis investigates why the flame speed increases dramatically with an increase in density of the powders. The investigation rests on the analytical model formulated by Makino by controlling how the variables are affected by changes in density. Flame speed measurements were performed in mixtures of nickel (Ni) and aluminum (Al) at different initial densities. The density was varied by controlling the cold-pressing of the samples inside metallic channels and tubes. Experiments were also performed in ball-milled powders, in order to permit comparison with the experiments performed by Bacciochini in these mixtures at nearly maximum densities. The measurements revealed that the flame speed increases with the initial density, with a discontinuous transition occurring at approximately 60% theoretical maximum density (TMD). This transition also corresponds to the point where the powders deform plastically during the compaction process, suggesting that the intimate contact between the particles is responsible for the flame speed increase. The flame speed dependence on powder density is attributed to the changes in the heat conductivity of the pressed powders. At high densities, where the powders have plastically deformed, the continuous structure yields conductivities close to the idealized solid matrix. At these high densities, the conductivity was modeled using the Effective Medium Theory (EMT). Analytical predictions of the flame speed, using available thermo-chemical data for the Al-Ni system were found in good agreement with the present experiments at high densities. At low densities, since Al-Ni is a mixture of loose powders, the EMT model is no longer applicable. Thus, the thermal conductivity was experimentally measured and then was fitted using the semi-empirical model suggested by Aivazov. Using this data, Makino's model predicts the correct flame speed dependence observed experimentally. The present thesis has thus established that the dependence of flame speed on density is due mainly to the changes in the structure and thermal conductivity of the powders.

No description available.

No description available.

There is an increasing trend towards advancing the understanding and development of ethylene oligomerization catalysts, both in academia and industry. The metal of choice in this chemistry is invariably chromium, which has shown great versatility in selective trimerization/tetramerization, non-selective oligomerization and polymerization of ethylene. While much success has been achieved in ethylene trimerization, the same con not be said about tetramerization catalysis. Aminophosphine based ligands have demonstrated their ability towards selective 1-octene production, however, the popular PNP catalyst is able to achieve only 70% selectivity. In order to explore the possibility of developing and enhancing the selectivity of chromium based ethylene tetramerization catalyst, this thesis work was undertaken. The ligand systems we chose for our work were bidentate aminophosphine based (PN(CH2)nNP), which has yielded interesting selective oligomerization. Subtle modifications were found to result in drastic changes in selectivity, from tetramerization (PN(CH2)3NP) to trimerization (PN(CH2)2NP). We managed to successfully develop the first truly selective (over 90%) 1-octene catalyst with polymer-free behavior. Further modifications on the ligand framework, where one atom of Si was used to link the two NP units, resulted in non-selective oligomerization, in which case we determined that the oxidation-state of chromium is a key player. We explored other modifications on our selective ligands in which one of the arms on the bidentate ligand was replaced with a base-donor amine, phosphine or pyridine, and resulted in interesting selectivity changes. The final modification that we tested was a novel N(CH2)2P ligand and found it to be a highly active, non-selective oligomerization catalyst.

There is an increasing trend towards advancing the understanding and development of ethylene oligomerization catalysts, both in academia and industry. The metal of choice in this chemistry is invariably chromium, which has shown great versatility in selective trimerization/tetramerization, non-selective oligomerization and polymerization of ethylene. While much success has been achieved in ethylene trimerization, the same con not be said about tetramerization catalysis. Aminophosphine based ligands have demonstrated their ability towards selective 1-octene production, however, the popular PNP catalyst is able to achieve only 70% selectivity. In order to explore the possibility of developing and enhancing the selectivity of chromium based ethylene tetramerization catalyst, this thesis work was undertaken. The ligand systems we chose for our work were bidentate aminophosphine based (PN(CH2)nNP), which has yielded interesting selective oligomerization. Subtle modifications were found to result in drastic changes in selectivity, from tetramerization (PN(CH2)3NP) to trimerization (PN(CH2)2NP). We managed to successfully develop the first truly selective (over 90%) 1-octene catalyst with polymer-free behavior. Further modifications on the ligand framework, where one atom of Si was used to link the two NP units, resulted in non-selective oligomerization, in which case we determined that the oxidation-state of chromium is a key player. We explored other modifications on our selective ligands in which one of the arms on the bidentate ligand was replaced with a base-donor amine, phosphine or pyridine, and resulted in interesting selectivity changes. The final modification that we tested was a novel N(CH2)2P ligand and found it to be a highly active, non-selective oligomerization catalyst.

There is an increasing trend towards advancing the understanding and development of ethylene oligomerization catalysts, both in academia and industry. The metal of choice in this chemistry is invariably chromium, which has shown great versatility in selective trimerization/tetramerization, non-selective oligomerization and polymerization of ethylene. While much success has been achieved in ethylene trimerization, the same con not be said about tetramerization catalysis. Aminophosphine based ligands have demonstrated their ability towards selective 1-octene production, however, the popular PNP catalyst is able to achieve only 70% selectivity. In order to explore the possibility of developing and enhancing the selectivity of chromium based ethylene tetramerization catalyst, this thesis work was undertaken. The ligand systems we chose for our work were bidentate aminophosphine based (PN(CH2)nNP), which has yielded interesting selective oligomerization. Subtle modifications were found to result in drastic changes in selectivity, from tetramerization (PN(CH2)3NP) to trimerization (PN(CH2)2NP). We managed to successfully develop the first truly selective (over 90%) 1-octene catalyst with polymer-free behavior. Further modifications on the ligand framework, where one atom of Si was used to link the two NP units, resulted in non-selective oligomerization, in which case we determined that the oxidation-state of chromium is a key player. We explored other modifications on our selective ligands in which one of the arms on the bidentate ligand was replaced with a base-donor amine, phosphine or pyridine, and resulted in interesting selectivity changes. The final modification that we tested was a novel N(CH2)2P ligand and found it to be a highly active, non-selective oligomerization catalyst.