The effect of time on the conversion of vanillin and distribution of products over ZCI (1,2,12)-700 at 130 ? and with hydrogen pressure of 0.7 MPa in water solvent was investigated as showed in Fig.
1. It would be seen that the conversion of vanillin increased dominantly in early 90 minutes. After 2 hrs reaction vanillin is converted completely with almost 90% creosol yield also small amount of HMP produced. In regard to HMP and MMP yield, it would be seems that in the first 90 minutes, MMP was most selective product and then HMP was generated with carried out the reaction. HMP yield changing trend was different as compared to MMP, which was indicated as intermediate product.
It is proved that there is no any other product detected in the entire process. That result indicates that carbonyl group of vanillin (C=O) mainly react with hydrogen to form HMP and after deoxygenation to form MMP in the water.The effect of solvent in reaction of vanillin hydrodeoxygenation and product distribution was studied over ZCI (1,2,12)-700 catalyst. Different five solvents tested, and the results were shown in Fig.2. Its seems that the highest conversion of vanillin and highest yield of MMP was obtained when using the water as a solvent.
The performance of THF, ethyl acetate and methanol are moderate with average yield of MMP. The n-hexane solvent showed very poor performance with conversion of vanillin and majorly yield of MMP. Solvents works as a media with much influences on mass transfer of products or reactants also donates proton to catalysis or involved in reaction of hydrogenation.
Here, we studied different solvents like polar protic, polar aprotic, borderline polar aprotic solvents and nonpolar solvents. We conclude that presence of N atom in the catalyst increases the hydrophilicity of ZCI (1,2,12)700 catalyst, which helps to increase the dispersion of catalyst in water. Because of dispersion exposure between catalyst and substrate improve. The reaction in methanol, ethyl acetate, n-hexane and THF produced relative very low conversion of vanillin (9.45-38.75%) with desired HMP and MMP products.There are different ZCI (Zn-Co-imidazole) catalysts is tested for the HDO of vanillin means imidazole supported Zn, Co catalyst with different Zn, Co and imidazole content were prepared, and results are shown in table 1. In a blank test, without any catalyst reaction carried out, almost no any transformation of vanillin.
Under the catalysis of ZCI (0,2,12)700, conversion of vanillin in water solvent was investigated and result could be seen that the conversion of vanillin is high but the selectivity of the MMP is very low. ZCI(0,2,12)700 catalyst only reduce the carbonyl group to alcoholic group. With the catalyst ZCI(1,2,12)WC and ZCI(1,2,12)500 there was no any conversion of vanillin. At 130 ? and with low hydrogen pressure of 0.7 MPa for 2 hrs, under the catalyst ZCI (1,2,12)700, the hydrogenation of carbonyl to HMP, followed by HDO of HMP to MMP was the predominant reaction pathway. Under the catalysis of ZCI(1,0,12)700 there is no any conversion of vanillin in water solvent. Although ZCI (0,2,12)700 similar vanillin conversion but the major product is HMP, which might be ascribed that Zn and Co both have important role for transformation of HMP. When the Co content increased to 4mmol in the ZCI (1,4,12)700 catalyst, the conversion of vanillin decreased.
The influence of reaction temperature on vanillin conversion under catalysis ZCI (1,2,12)700 in water solvent was investigated and results were shown in Fig. . The conversion of vanillin seen that >99.5% at 90 ? to 150 ? but variation of MMP yield. The effect of temperature clearly showed that conversion of vanillin to have two steps but with increasing temperature rate of reaction increased at constant pressure and time. The effect of feed ratio of vanillin to catalyst on vanillin conversion and products distribution was studied over ZCI (1,2,12)700 catalyst in water solvent. Results shown in Fig. .
It would be seen that 10 mg and 30 mg catalyst shows very low conversion of vanillin but at 50mg the conversion of vanillin was >99.5 and MMP yield also increased up to 89.1%. At 75mg catalyst the vanillin conversion was >99.
5 and selective MMP product.The stability of ZCI (1,2,12)700 catalyst was also studied for HDO of vanillin and catalyst recycled for 5 times. After reaction every time catalyst was separated and washed with DCM and water then dried in oven at 80 ? without other treatment. Table. .
showed the change of vanillin conversion and change of HMP and MMP yields with different recycle run of catalyst. It could be observed that with increasing recycle run of catalyst, the conversion of vanillin decreased from >99.5% to 39.4%. It means that catalyst lost its ability slightly with increasing of cycles. Also, the yield of MMP decreased gently from 89.
1% in first run to17.3% in fifth run, while the yield of HMP increased from 10.8% to 21.9%. It means that hydrogenolysis of HMP to MMP slightly decreased.
It could be happened may be because of changes in the catalyst surface. It could be seen the ability of ZCI (1,2,12)700 for hydrogen transfer on the different unsaturated hydrocarbon bio-molecules are investigated in Table. As a lignin derived product, selective hydrodeoxygenation of syringaldehyde is carried out. It could be found that 97.68% conversion is obtained with 100% selectivity of 4-Methylsyringol at 130 ? in 2 h reaction (entry 1).
Other bio-molecule containing ketone functional group, such as acetovanillone (entry ), affords the corresponding hydrocarbon with low conversion without any side product. In case of 3(4-hydroxy-3 methoxyphenyl)-1- propanol no any conversion at130 ? in 2 h reaction (entry ). Next, after pyrolysis of lignin most of the product obtained, 2-phenoxy-1-phenylethanol is one of it. Hydrodeoxygenation of 2-phenoxy-1-phenylethanol gives 84.93% conversion with 100% selectivity of 1-phenethoxybenzene (entry ).