Morphology Control In Synthesis Of The Titanate Nanofiber And Its Application As A Solid Base Catalyst

The elongated titanate fibers（TiNFs） can be applied as catalystsupports due to their high BET surface area as well as their non-porousfiber structure which bring them the advantages on aspect of thermalstability, mechanical strength and mass transfer rates over the hollow fibercounterparts. This thesis is probing the application of titanate fibers as thesupport for a solid base catalyzed reaction.First selectively synthesized the non-porous TiNFs support, where theinfluences of titanium precursor, base solution type and temperature ofhydrothermal reaction on morphology and pore sized distribution of theresulting TiNFs were investigated. The synthesized titanate fibers, asexamined by TEM, SEM and BET&BJH，were featured by diameter70~100nm, length tens to hundreds microns, with the length to diameterratio up to1000, and BET specific surface area and pore volume up to311m2/g and0.597ml/g, respectively，while the XRD pattern of TiNFs wasidentified as K2Ti8O17. It was found that the TiNFs made from amorphous titania gel werefeatured by wide diameter and short length, the length to diameter ratioaround500, but found no difference in BET specific surface area. Theinfluence of base type is different for different precursors: for TiNFs fromP25, the pore structure is changed by base type; while for TiNFs fromtitania gel, the morphology and size. When the pretreated precursors werekept at lower hydrothermal temperatures, the obtained TiNFs are longerbut with the same pore structure. The TGA test found no decomposition ofTiNFs at high temperatures, and the fiber morphology were stable with nosinter or collapse or change in length after calcination at400℃.At last, taking TiNFs as the support and modified by doping orimpregnation of KF as the base catalyst for synthesis of propylene glycolmonomethyl ether (PM) through methanolysis of propylene oxide (PO).The KF doped catalysts have demonstrated a PO conversion of99.17%and a selectivity to1-methoxy2-propanol(PPM) as93.38%. The POconversion and PPM selectivity were97.85%and92.91%, respectively forcatalysts made by impregnation method, which were much higher than theblank support. It was also found that catalyst performance was decided bythe washing procedure. The CO2-TPD test proved that the total amount ofbase sites in the KF doped KF/TiNFs catalyst was over twice of that in the blank TiNFs, and the medium strength base sites found only in the formercatalyst is main source of activity. The stability test found that the activityof the catalyst reduce slowly in the first three times of repeated usage, butthen abruptly reduced. After5times usage, the PO conversion reduced to27.94%and PPM selectivity89.59%for the same batch of catalyst. Thecatalyst used for5times was regenerated by calcination at400℃in airwhose PO conversion resumed to92%and PPM selectivity90.6%. Thedeactivation is therefore proved mostly due to the coverage of the activesites by organic compounds, partially by leaching.