Investigation On Preparation And Liquid Hydrogenation Of Maleic Anhydride Of Highly Dispersed CuZnTi Catalyst Derived From Layered Double Hydroxides

Supported metal catalysts are one of the most important catalysts used in oil refining and petrochemical processes, which are widely used in hydrogenation, dehydrogenation and re-engineering and other catalytic reactions. Supported metal catalysts not only have highly activity and selectivity, but also have advantages of stability, easy to regeneration and reuse. In present paper, carbonate intercalated CuZnTi layered double hydroxides (CuZnTi-LDH-CO3) were firstly synthesized, and then used as precursors to obtain a series of highly dispersed CuZnTi catalysts. The crystal structure, composition, dispersity and nature of the catalytic active site were systematically characterized by using XRD, ICP, FT-IR, SEM/ EDS, TEM/HRTEM, BET, H2-TPR/TPD and XPS techniques. Liquid phase hydrogenation of maleic anhydride was carried out over the catalysts to invest the catalytic activity. The natural relationship between the structure and catalytic properties of the prepared catalysts were studied carefully. The novelty and major content of the thesis were presented as follows:The LDH catalyst precursors CuZnTi-LDH-CO3 with varied Cu content have been synthesized by both one-step coprecipitation with constant pH value (CLDH) and urea hydrolysis (ULDH) methods. The crystallinity of the as-prepared LDH are gradually increased with increasing contents of Cu species (10.0 wt%-36.2 wt%). While the average size of LDH-like sheet synthesized by one-step coprecipitation method is about 200 nm, much smaller than that of the ones obtained by urea hydrolysis method (500-1000 nm). The XRD results show that the crystal structure of the U3LDH with higher Cu content (43.8 wt%) is mainly Cu(OH)2. A series of CuZnTi catalysts are obtained by proper calcination of the series precursors. The C-catalysts (derived from CLDH) present as homogeneous mixed oxides containing amorphous TiO2, monoclinic CuO and hexagonal ZnO, while the U-catalysts consisting of anatase TiO2, monoclinic CuO and hexagonal ZnO. The C-catalysts (C0.5-C2) are partially aggregation spheres with particle size 20-30 nm and after H2-activation the gap between the catalyst grains increased and show more uniform distribution. The U-catalysts (U1 and U2), inheriting the character of the precursors, are flake-like particles (500-1000 nm) orderly aggregated by the small grains (25-30 nm) and after the H2-activation, slight collapse of the layers occurred. However, the U3 catalysts are disorderly distributed particles with spherical, rodlike and flake-like morphology and the aggregation extent increased after the H2 activation.The catalystic activity and the selectivity of the highly dispersed CuZnTi catalysts in maleic anhydride liquid hydrogenation to y-butyrolactone were studied under different reaction conditions. In an optimum reaction conditions (H2 pressure:2.0MPa, reaction temperature: 200℃and reaction time 2 h), the C2-catalyst shows the best catalytic activity among all of the C-catalysts, with the conversion of maleic anhydride approaching 100% and y-butyrolactone selectivity of 83%. While the catalytic activity of U-catalyst is greatly decreased, and the U3 shows the lowest catalytic activity.Combined the HRTEM, XPS and H2-TPR analysis with reactivities, the high activity of the C-catalyst can be attributed to the small-sized uniform mixed oxides particles featuring as highly dispersed active metal Cu on the amorphous TiO2 doped CuO-ZnO originated from the LDH-type layered precursor. We tentatively proposed the catalyst structure models of the highly dispersed CuZnTi catalysts obtained by both layered precursor methods.