Sodium Phosphomolybdate Modified LDHs For Catalytic Properties In α-pinene Oxidation

a-Pinene is the main component of turpentine oil and thus is a readily available, inexpensive and renewable starting material. Its oxidation products are of high practical importance. Now, much effort in the a-pinene oxidation reaction has been mainly devoted to the survey of the new recyclable catalytic system with the environmentally friendly oxidants. In recent years, Layered Double Hydroxides (LDHs) have attracted an increasing attention in many organic reactions owning to their unique structure and properties. This dissertation adopted co-precipitation method microwave-assisted method in the crystallization of the samples prepared the hydrotalcite containing titanium of surface and interlayer sodium phosphomolybdate modification. The LDHs samples crystallinity, mode of action of interlayer anions, morphology, thermal stability property, particle size and distribution are explored. We used a-pinene as probe substrates in order to investigate the catalytic performance of sample LDHs using30wt%H2O2as oxidant in the absence of cocatalyst under mild conditions. A lot of experiments were done to analyze and compare the results to explore the influence of catalysis.(1) The sodium phosphomolybdate (SP) intercalated into a binary Mg-AI and a three-element Mg-Ti-Al, layered double hydroxide (LDHs/SP) were prepared by co-precipitation method microwave-assisted method in the crystallization of the samples, which were denoted as Mg-Al-LDHs/SP and Mg-Ti-Al-LDHs/SP, respectively. Then the samples characterised by various physicochemical techniques, including powder X-ray diffraction, SEM and FT-IR analysis. The results showed that LDHs/SP were a thickness of10-20nm, lateral dimension200～500nm nano convoluted flexible sheet product consisting of intertwined, with complete structure and high crystallinity. The activ, and selective of heterogeneous catalyst for epoxidation a-pinene were investigated by using30wt%hydrogen peroxide as oxidant and CLDHs/SP (LDHs/SP calcined in673K for4h) as catalyst. The results suggest that the optimum reaction conditions were:reaction time=5h, reaction temperature=60℃, the reaction solvent is Vacetone:Vwater=3/7(Total2ml), the conversion of a-pinene could reach to73.8%.(2) The sodium phosphomolybdate surface modified hydrotaleite containing titanium, zinc, aluminium and carbonate were rapidly synthesized by surface deposition, which were denoted as Zn-Ti-Al-LDH/SPs, Zn-Ti-Al-LDH/SP10, Zn-Ti-Al-LDH/SP,5, Zn-Ti-Al-LDH/SP20and Zn-Ti-Al-LDH/SP25, respectively. The experiments showed that the optimal activation index modification reaction conditions are as follows:time40min, temperature70℃, optimum amount of modifier is15%. XRD showed that the sample has a characteristic structure of the hydrotalcite, IR characterization to determine the presence of a phosphorus molybdate. SEM characterization implies the change of particle size and distribution occurred with the sodium phosphomolybdate content increasing, the agglomeration of LDHs surface became much worse. ICP-AES characterization showed the proportion of Mo and Ti in the sample. TG-DTG analysis showed that the existence of SP impact the thermal decomposition rate of the sample, the maximum thermal decomposition rate increases nearly50℃, and enhanced the heat resistance of hydrotalcite.(3) The effect of reaction time, reaction temperature, catalyst concentration, n(H2O2):n(a-pinene), solvent on the catalytic performance using Zn-Ti-Al-LDH/SP15as catalyst were investigated. If the reaction time was extended from60min to480min at70℃, the conversion of a-pinene could increase7.0%and the selectivities of main products increase, while the selectivity of byproducts decrease. When the reaction temperature was increased from333K to373K, the conversions of a-pinene were improved2.3%, with the selectivity of a-pinene epoxide increased by3.0%. If we increased the concentration of H2O2, both the conversions of a-pinene and the selectivities of rearrangement products were increased, whereas the selectivity of a-pinene epoxide decreased. Experimental results show that the optimum concentration of catalyst was0.4g/L. The catalyst (Zn-Ti-Al-LDHs/SP15) could be recycled used four times and its conversion rate still could reach50.2%.