Preparation Of A Cage Like Ni-based Catalyst And Its Application In Bio-oil Upgrading

Bio-oil derived from fast pyrolysis of biomass is widely regarded as one of the most potential renewable energy. However, bio-oil needs to be further improved because of its high oxygen content, high water content and unstability. At present, commonly used catalysts for bio-oil hydrogenation are supported nano-catalysts. There is a problem that the active particles of the nano-catalysts are easily sintered under high temperature. Therefore, in our work, we designed and prepared a cage-like catalyst Ni/C-Si O2-Al2O3(denoted as Ni/CL-CSA). Phenol was chosen as bio-oil model compound to evaluate the hydrogenation performance of the catalysts. Furthermore, the catalyst was used to upgrade the bio-oil. The results are as follows.1. A cage-like nickel-based catalyst Ni/CL-CSA is successfully synthesized via a facile dual-templating method using resols, tetraethoxysilane(TEOS) and aluminum chloride hexahydrate as C, Si O2 and Al2O3 source, in which polystyrene(PS) colloid is selected as macroporous template and Pluronic F127 as mesoporous template. Characterization results show that the Ni/CL-CSA have about 100 nm cage size and about 3.8 nm window size. Nickel nanoparticles are about 6 nm. BET surface area of Ni/CL-CSA is 212 m2/g and total pore volume is 0.24 cm3/g. A mesoporous catalyst Ni/C-Si O2-Al2O3(denoted as Ni/MP-CSA) with straight channels for comparison is also prepared. It has an ordered two-dimensional hexagonal structure with mesopores of 4 nm, pore wall thickness of about 6-8 nm, nickel particle size of around 6.5 nm. BET surface area of Ni/MP-CSA is 219 m2/g and total pore volume is 0.24 cm3/g.2. We use phenol as bio-oil model compound to investigate the activity and stability of the catalysts. Results imply that Ni/CL-CSA shows higher activity than Ni/MP-CSA. When the reaction was carried out for 5 h, the conversion rate of phenol over Ni/CL-CSA and Ni/MP-CSA is 100% and 97.3% respectively. At 3 h, the conversion rate of phenol over Ni/CL-CSA reached 88.3% and the conversion rate of phenol over Ni/MP-CSA is 62.2%.This may be because incorporation of macroporous cages into mesoporous catalyst promotes the transmission rate of matter, in turn, promotes the conversion of phenol. Moreover, the thermal stability of the catalyst is also investigated. After 600 ℃ heat treatment for 5 h, the conversion rate of phenol over Ni/CL-CSA 600 remained 80.3% while Ni/MP-CSA 600 dropped to 49.6%. According to the results of XRD, the cage like structure of Ni/CL-CSA prevents particles from aggregation and thus keeps the activity and stability of the catalyst.3. We investigated upgrading of bio-oil over Ni/CL-CSA catalyst at 200 ℃, 240 ℃ and 280 ℃. The results show that after adding Ni/CL-CSA, the coke decreased by 4.6%, 4.6% and 7.3% respectively. GC-MS analysis shows that the contents of acids decreased from 2.5% to 1.2%, furans decreased from 6.1% to 1.3%. The upgrading products are mainly composed of relatively stable components, i.e. alcohols, esters, ketones and hydrocarbons. So the stability of upgraded bio-oil is enhanced.