| Based on the efficient energy utilization, environmental protection andpolicy response, our research group combines the huge CH4resources with thebiggest domestic pollutant emissions of CO2, developing a technology with lowenergy cost and non-oxide of directing synthesis of acetic acid with CH4andCO2. Furthermore, we designed continuous step-wise reactor and determined theCo-Pd metals as the active components, TiO2as good carrier of catalytic system.On the basis of previous studies, learning much from our former member Sun’sprocess conditions, the influence of the catalysts by sol-gel method on thesynthesis of acetic acid with CH4and CO2was systematically investigated.Besides, the carrier of TiO2was modified by Al2O3.The activities of all thecatalysts were evaluated in the own-designed continuous step-wise reactor andfurther characterized by the techniques of XRD, NH3-TPD-MS, XPS, BET andFT-IR in order to clarify the relationship between the structure and catalystperformances. The main research results are as follows: (1) The prepared catalysts using titanium isopropylate as the source of Tihad stable pore structure, of which the catalytic activity was better than usingP25and tetrabutyl titanate as the sources of Ti.(2) Suitable amount of weak and medium-strong acid sites will be conduci-ve to the formation of C2oxygen-containing compounds. Which selectivity ismainly affected by the amount of acid, relatively large amount of acid can pro-mote the yield of acetic acid.(3) The relative larger pore size can reduce the internal diffusion resistance,speed up the mass transferring, diffusion of reactants and products, and thus canenhance the step reaction rate of CH4and CO2. And larger average pore size helpto improve the selectivity of acetic acid.(4) The optimal pH value of sol-gel method was1at which preferred catalystactivity and stable crystal structure were obtained.(5) The high selectivity of ethanol and acetic was obtained by usingCo-Pd∕TiO2-Al2O3in the step-wise reaction. When the content of Al arrived at10%, the catalyst showed the best catalytic activity. The total formation rate ofethanol and acetic acid reached the point of13.39mg g-1-cat. h1. Compared withthe catalyst prepared by single source of Ti, the catalytic activity increased by2.87times.(6) Not only the addition of10%Al content, pH=1, but also loadings of7%Co and3.5%Pd can promote the balance distribution of the active metals, whichmakes the ratios of active metals in the catalyst surface closing to the ratios of initial materials, satisfying the activation of CH4and the insertion of CO2conductedsimultaneously, which shows better catalytic activity.(7) In the composite carriers with TiO2and Al2O3,the forming chemicalbond of Ti-O-Al can change the qualitative of acidic, increase the amount ofmiddle-strong acid site, speeding up the activation of methane.(8) The method of sol-gel to prepare different loadings of Co-Pd catalysts issimilar to that of impregnation, with which the best load is7%Co and3.5%Pd,too big or too small of the loadings will not be conducive to the formation of C2oxygen-containing compounds. |
PDF Full Text Request