(591c) Nano Core-Shell Structured ZSM-5@Mesoporous Silica for Catalytic Co-Cracking Phenolic Bio-Oil Model Compounds and Ethanol to Aromatics

As the depletion of fossil fuels and severe pollution caused by the excessive usage become an upcoming threat, looking for alternative and green energy sources is an urgent matter for sustainable development. Lignocellulosic biomass can be converted to fuels and aromatics as industrial chemicals and the essential additive in jet fuel through feasible methods, such as fast pyrolysis. However, because of its high content of phenolic compounds, the upgrading of this kind of bio-oil remains as a big challenge. Co-cracking raw bio-oil with alcohols is considered to be an effective method. But the conventional catalyst ZSM-5 shows an unsatisfied catalytic performance and still needs to be improved. The fast deactivation of catalysts caused by severe coke formation on the catalyst particles’ surface and the low selectivity of desired aromatics product are the biggest issues.

The nano-sized molecular sieve catalysts have showed a better performance in many areas because of its bigger surface area and improved diffusion of reactants and products. Also the core-shell structured ZSM-5 with mesoporous shell has proved its potential in adsorption, hydrocracking, and supercritical catalytic cracking and so on. However, when combining the two techniques together to rebuild ZSM-5, more studies need to be done to reveal the influence of the catalyst properties on catalytic performance. Here, the effect of mesoporous shell and crystal size on the conversion of bio-oil and selectivity over aromatics products is studied by preparing nano ZSM-5 with different size by seed-induced method and core-shell composites by a simple hydrothermal treatment in alkaline solution with cetyltrimethylammonium bromide (CTAB), noted as ZSM-5@meso SiO₂. The size of synthesized composites are about 350nm, 700nm and 1μm, respectively. And the thickness of mesoporous silica shell is about 25nm. Six model compounds were used to represent the phenolic pyrolysis bio-oil, and then mixed with ethanol. The mixture had 50wt% of ethanol, 25wt% of phenol, guaiacol and eugenol, and 25wt% of acetic acid, hydroxyacetone and methylfuran. The conventional ZSM-5(Si/Al=50) had only 4.47% (GC-MS peak area %) of BTX products and 83.27% of phenolic products. While the nano ZSM-5 had much higher selectivity on aromatic and BTX, up tp 75% higher than those of ZSM-5. And eugenol can be completely converted. By tailored with the mesoporous shell, the ZSM-5@meso SiO₂ can effectively suppress the selectivity of PAH. The ratio of MAH to PAH for core-shell structure was about 20% higher than those of catalysts not tailored. Under a typical reaction condition(450℃, WHSV=2h^-1), the nano core-shell ZSM-5@meso SiO₂ could have a selectivity of 24.39% over aromatics and only 55.3% over phenolic products, with guaiacol and eugenol completely converted. The improved catalytic performance of nano core-shell composites can offer a new route for designing novel cracking catalysts with better resistance to coke formation and higher hydrocarbon selectivity.