Catalytic Oxidation And Hydrolysis Of HCN Over La-Cu/TiO₂ Catalysts At Low Temperature

Hydrogen cyanide?HCN?is a typical unconventional atmospheric pollutant with flammability and toxicity.Hydrogen cyanide exist in many industrial processes and the processing of nitrogenous materials.The presence of hydrogen cyanide in the exhaust will not only restrict the resource utilization of industrial tail gas and affect the purification of other pollutants,but also cause serious damage to the ecological environment.Based on the research status of hydrogen cyanide purification at home and abroad as well the demand for optimizing the process section and energy saving and emission reduction in practical industrial applications,we carried out the research on catalytic hydrolysis and oxidation cyanide hydride at low temperatures.The HCN conversion of Catalytic hydrolysis and oxidation was the highest,which reached 60.22%at a low temperature of 100°C,and the conversion of HCN and the selectivity of N₂ were as high as 100%and 62.24%at 150°C,respectively.In this paper,a series of bimetallic active component catalysts supported on titania were prepared by sol-gel method for catalytic hydrolysis and oxidation of HCN.The La-Cu/TiO₂ catalyst has the best HCN catalytic activity by comparing the activities of different catalysts.We further optimized the ratio of La/Cu in the catalyst,and indicated that a small amount of La ₂O₃ improved the catalytic activity significantly.The catalyst calcined at 450°C has the highest HCN catalytic activity and optimal microstructure.In addition,the reaction temperature and the operating parameters during the preparation of the catalyst by the sol-gel method have a great influence on the catalytic activity of HCN.In order to explore the effect of pH of sol on the catalytic activity of La-Cu/TiO₂catalyst by sol-gel method,La-Cu/TiO₂ catalysts with pH=2,4,6,7,8,10 and 12were prepared under different pH conditions.The results of the activity experiments showed that the catalyst with pH=10 had the best catalytic activity,while the activity of the catalyst with pH=4 was very close to that of the pH=10.Catalysts under neutral conditions are the least active.N₂ adsorption-desorption?N₂-BET?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,temperature programmed reduction?H ₂-TPR?,temperature programmed desorption?CO₂/NH₃-TPD?And Fourier transform infrared spectroscopy?FT-IR?characterization techniques are performed to explore the microstructure of the catalyst,such as pore structure and crystal form,as well as the physical and chemical properties of the surface.NH ₃-SCR experimental results and characterization results were for deducing the reaction process and mechanism.According to the results of H₂-TPR,XRD and XPS,after adding a small amount of La to the Cu/TiO₂ catalyst,a strong interaction between La and Cu oxide was formed.This interaction formed a rich oxygen hole,thus promoted high dispersion of the active component on the catalyst and increased the redox of the La ₁Cu₉/TiO₂ catalyst.And a small amount of La₂O₃ increased the total acidity of the catalyst surface,allowing the catalyst to have more moderately acidic sites at lower temperatures.This is also the reason for the higher HCN conversion and N ₂ selectivity at low temperatures.During the preparation of the catalyst by sol-gel method,the pH played an important role on the hydrolysis and polycondensati on process of tetrabutyl titanate,which then affected the microstructure and chemical properties of La-Cu/TiO₂ catalyst.The catalysts with pH=10 and 4 have stronger low-temperature redox properties,optimal microscopic pore structure and optimal composit e crystal form?anatase and rutile?.In addition,the catalyst with pH=10 has the most strong acidic sites.The results of NH₃-SCR tests shown that La-Cu/TiO₂ catalyst had better low-temperature selective catalytic reduction of NOx,and a part of N ₂ in the product was derived from the process of NH₃-SCR.