Sythesis of mesoporous phosphates via solid state reaction at low temperature

Qi Liu, Purdue University

Abstract

Three parts consist of my thesis work centered on the synthesis of inorganic phosphates and then metal organic frame work (MOF). The first part is the synthesis of mesoporous chromium phosphates using the room temperature solid state reaction (SSR) approach. One of the major aims of this work is to fill the gap of lacking a low cost, low or zero pollution, easy method to synthesize phosphates. The room temperature solid state reaction has been demonstrated in this work is such a method. Mesoporous chromium phosphates were prepared using the solid state reaction at low temperature using CrCl3·6H 2O, and NaH2PO4·2H2O as precursors and the surfactant CTAB as template. The synthesized chromium phosphates were characterized by XRD, EDS, HR-TEM, N2-physisorption, TG-DSC and UV-Vis spectroscopies. The results indicate that chromium phosphate mesophases were formed only at atomic ratios of P/Cr >1.8. The mesophase for P/Cr = 2.0 phosphate possessed the highest ordering of pore array, with a specific surface area as high as 250.78 m2/g and an average pore size of 3.48 nm. The catalytic performance of the chromium phosphates was examined by employing a model reaction, namely the dehydration of isopropanol to propene. The results indicated that all synthesized chromium phosphates exhibited significantly higher isopropanol conversions and propene yields than that synthesized via the conventional precipitation route. The highest propene selectivity (96.43%) at the highest isopropanol conversion (93.10%) has been obtained over the mesoporous chromium phosphate catalyst synthesized with a P/Cr atomic ratio of 2.0. The formation mechanism of the mesoporous chromium phosphate was investigated by FTIR technique. The results show that CTAB template plays a key role in the formation of mesoporous chromium phosphates. Mesoporous lithium manganese phosphates were also successfully synthesized using the same approach of solid state reaction (SSR) at low temperature by using LiC2O3·6H2O, MnCl2·6H 2O and NH4H2PO4·2H2O as precursors and the surfactant cetyltrimethyl ammonium bromide (CTAB) as template. The synthesized lithium manganese phosphates were characterized by XRD, EDS, SEM, HR-TEM, N2- physisorption. The results show that the synthesized meoporous lithium manganese phosphates exhibited a high specific surface area (256.63 m2/g) and a narrow pore size distribution. The electrochemical tests of Li-ion batteries were performed and the results show that the charge voltage could increase to be 3.60 V while the first time discharge capacity could be as high as 100 mAh/g. The Nitro-Cu-MOF complexes, a new class of metal organic frameworks, have been successfully synthesized using a conventional thermal reaction. The obtained Nitro-Cu-MOFs have a specific surface area of 576.27 m 2/g and a pore volume of 0.32 m3/g. The gas uptake of the obtained Nitro-Cu-MOFs at 60 psi is 68 mg/g (sorbate/sorbent) at 298 K for carbon dioxide, which is much higher than that of the Cu-MOFs, 31 mg/g at 298 K for carbon dioxide.

Degree

M.S.M.E.

Advisors

Xie, Purdue University.

Subject Area

Mechanical engineering

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