Preparation Of Copper Based Compounds For Catalytic Oxidation Of Glycerol

With the excessive consumption of traditional fossil energy,biodiesel as a renewable liquid fuel has received extensive attention.However,a large amount of low value-added by-product glycerol is produced in the process of biodiesel production,and its random disposal not only brings serious environmental problems,but also is a waste of resources.To promote the wide application of biodiesel and the effective utilization of excess resources,it is thus of great theoretical significance and practical value to convert glycerol into high value-added products.Among many methods of glycerol conversion,catalytic oxidation is an effective method to convert glycerol into high value-added products.At present,most of the catalysts used in the research of glycerol oxidation are noble metal catalysts.Although they have excellent activity and high product selectivity,noble metals are easily poisoned by the strong adsorption of carbon-oxygen intermediate species formed by excessive oxidation of glycerol,which are not conducive to large-scale application due to high cost and small reserves.Therefore,the development and design of inexpensive and efficient non-precious metal catalysts is the key to catalyze the continuous oxidation of glycerol.Based on this,in this thesis,copper based catalysts with catalytic activity were selected from transition metals through a series of glycerol oxidation activity tests,and their structural design and performance optimization were studied.The main research contents and conclusions are as follows:1.Taking common transition metal oxide catalysts NiO,CoO,CuO catalysts and commercial Mo₂C with Pt-like noble metal properties as the research objects,the catalytic performance of the catalysts was evaluated by glycerol oxidation reaction.The results showed that only Cu-based catalysts had the ability to catalyze the oxidation of glycerol.The conversion rate of glycerol oxidation was 43.73%,and the resulting products were mainly formic acid（66.66%）and glyceric acid（23.9%）,and a small amount of glacial acetic acid（5.02%）and glycolic acid（4.41%）.It was found by XRD characterization that the catalyst existed in the coexistence form of basic nitrate or carbonate and copper oxide,rather than the common oxides like other transition metals.Therefore,in the follow-up work,copper-based oxide catalysts containing basic salts will be the object of further research on catalytic glycerol oxidation.2.Copper chloride was selected as copper salt,potassium hydroxide and potassium carbonate as precipitants,and Cu₂（OH）₂CO₃-CuO catalyst was prepared by solid-phase grinding precipitation method,and annealed at different temperatures.The catalytic performance of the catalyst for glycerol was studied by physical characterization and glycerol oxidation test.The results showed that the copper-based compounds prepared by solid-phase grinding precipitation method were mainly CuO with poor crystal form,and Cu₂（OH）₂CO₃ was highly dispersed in CuO in amorphous form,which had high specific surface area and was helpful to expose more active sites.Among them,CuO was the main active center,and Cu₂（OH）₂CO₃ acted as the second active center to synergistically catalyze the oxidation of glycerol,showing excellent activity in the reaction,and the conversion rate of glycerol was 55.06%.The catalyst was reduced at 400℃,and the obtained Cu catalyst maintained the original catalytic activity while the stability was effectively improved.3.In order to further improve the activity and stability of Cu₂（OH）₂CO₃-CuO bulk catalyst,this chapter introducedγ-Al₂O₃ carrier in the preparation process of the above catalyst,and Cu₂（OH）₂CO₃-CuO was highly dispersed on Al₂O₃ by solid-phase grinding precipitation method.The experimental results showed that the introduction of supportγ-Al₂O₃ could not only improve the stability of the catalyst,but also the acidic sites on its surface had a synergistic catalytic effect.The 5%Cu₂（OH）₂CO₃-CuO/Al₂O₃ catalyst had the most excellent catalytic activity,and the glycerol conversion rate increased to 62.97%.This was because the high dispersion of Cu₂（OH）₂CO₃-CuO in the catalyst with small particles,and it was not easy to block the pores of the carrier.So,the specific surface area of the catalyst was similar to that of the unsupported carrierγ-Al₂O₃.At the same time,the loading of Cu₂（OH）₂CO₃-CuO was relatively low,which would not occupy a large amount of the acidic sites ofγ-Al₂O₃,soγ-Al₂O₃ could cooperate with Cu₂（OH）₂CO₃-CuO active center to improved the conversion rate of glycerol oxidation.In order to verify the synergistic effect of the acid sites ofγ-Al₂O₃,the5%Cu₂（OH）₂CO₃-CuO/Al₂O₃ catalyst was reduced in H₂/Ar mixed atmosphere.As the surface properties of the carrier Al₂O₃ changed during this process,the synergistic effect of the carrier decreased significantly.Therefore,the activity of5%Cu₂（OH）₂CO₃-CuO/Al₂O₃-400℃-H₂ catalyst was not as good as the catalyst obtained by direct annealing treatment.