Design For Novel Nanometer Magnetic Composite Catalysts And Its Synthesis & Structure-Porpetty Investigation

An effective combination of a series spinel ferrites and LDHs layered materials to form core-shell structured nanometer magnetic catalytic materials has been designed and realized in this thesis.Firstly, a series of spinel ferrites MFe2O4(M=Mg, Ni, Co,(NiZn)) with different magnetization were synthesized by LDHs-based layered precursor method, and characterized by XRD, IR, laser particles size distribution (PSD) analysis and vibration sample magnetization(VSM) measurements. The results show that as-synthesized Mg, Ni, Co and (NiZn) ferrites present well-defined spinel structure with particle size distribution at 34-125 nm, and optimum particle size of ca. 62-64 nm. The specific saturation magnetization ((s) of Mg, Ni, Co and (NiZn) ferrites are 27.0, 32.3, 60.6, and 5.4 emu/g, respectively, and the first two samples give zero coercive force, behavioring soft magnetism, the third one gives higher coercive force due to hard magnetism of CoFe2O4 and the last one only shows small (s value and zero coercive force, clearly presenting as weak magnetic ferrites.A combination of LDHs materials and a series of ferrites were carried out through a method involving separate nucleation / aging steps. The initially formed MgAl-CO3-LDHs/MFe2O4 precursors were then undertaken calcinations and rehydration procedures to give oxide-type catalysts MgAl(O)/MFe2O4 and hydroxyl-type catalyst MgAl-OH-LDHs/MFe2O4, respectively. The XRD, IR, TG-DTA, BET, CO2-TPD, XPS, TEM, VSM and PSD analysis were employed to characterize the catalysts. The results show that the combination of LDHs material and spinel ferrites succeeded in forming a composite-type catalyst with reasonable structure-property relationship. Very importantly, XPS and TEM results demonstrate the obvious core-shell structure of magnetization of MgAl-OH-LDHs/MgFe2O4. The reduction of specific saturated magnetization of MgAlOH-LDHs/MgFe2O4 is ascribed to the shield from non-magnetic LDHs layers. MPV and DMC reaction were used to test the catalytic properties of novel catalysts MgAl(O)/MFe2O4(M=Mg, Ni, Co). The results show the higher catalytic properties. MgAlOH-LDHs/MFe2O4 (M=Mg, Ni, Co and NiZn) have shown the same considerable DAA conversation as compare to the literature values in the actone self-condensation reaction. Especially MgAl-OH-LDHs/MFe2O4 (M=Mg, Ni, Co) can be reclaimed more than 94% through an exterior magnetic field of 0.0427 T. The novel catalysts have realized the effective assembly of catalytic property and magnetization. Two possible core-shell structure models have been proposed based on structure-property investigation.