Transition metal loaded aluminophosphate molecular sieves

Abstract

In this thesis, the synthesis and characterization of the transition metal loaded AlPO4-5 catalysts are described. The catalytic properties of these catalysts were studied. The adsorption and decomposition of Mo(CO)6, Co2(CO)8, Co(CO)3 NO and Fe(CO)5 in AlPO4-5 have been followed by gravimetric and infrared techniques. Mo(CO)6, Co(CO)3 NO and Fe(CO)5 adsorbed readily in the channels of AlPO4-5 whereas a large proportion of Co2(CO)8 adsorbed on the external surface of the channels. Activation of Mo(CO)6, Co(CO)3NO and Fe(CO)5 adsorbed onto AlPO4-5 in vacuum by heating to 673K retained and decomposed only a fraction of the initially adsorbed carbonyls in AlPO4-5. The percentage retention of the initially adsorbed Co2(CO)8 however is much higher than the other three carbonyls, as a result of more effective pore mouth blocking of the externally adsorbed Co2(CO)8 and Co4(CO)12. The carbonyl adsorption studies showed that less subcarbonyls were produced in AlPO4-5 at room temperature than in zeolites. Except for Co2(CO)8, heating the carbonyl adsorbed AlPO4-5 samples in vacuum caused decomposition to occur directly to the metal. Co2(CO)8 adsorbed on the external surface of AlPO4-5 decomposed to Co through the formation of Co4(CO)12. Zerovalent metal particles were produced after decarbonylation of the adsorbed carbonyls. O2- was formed in AlPO4-5 when in contact with O2. O2- showed anomalous rotational behaviour at different recording temperature. CO hydrogenation reaction was studied on these catalysts using both recirculating and flow reactor systems. For Mo-AP-5, Co-AP-5 (Co(Co)3No) and Fe-AP-5 catalysts, the results showed that they are at least as active as their corresponding zeolite catalysts. Mo-AP-5 catalyst yielded predominantly alkanes whereas Fe-AP-5 catalyst gave high yield of alkenes. Co-AP-5 (Co(CO)3NO) catalyst gave a moderately high propene yields, but the alkane yield especially that of CH4 was also high. The Co-AP-5 (Co2(Co2(CO)8)catalyst however, deactivated rapidly as the reaction time increased. The catalytic activity and selectivity of all the catalysts were correlated to the metal particle size and dispersion.