Fractional factorial study of HCN removal over a 0.5% Pt/Al ₂O ₃ catalyst: Effects of temperature, gas flow rate, and reactant partial pressure

Hydrogen cyanide (HCN) oxidation under lean conditions was studied on 0.5% Pt/Al ₂O ₃ catalysts. Fractional factorial design was used to determine which factors had significant effects on HCN conversion in these experiments. We conclude that reaction temperature and gas hourly space velocity (GHSV) had the most significant effects on HCN conversion, whereas no significant effects were caused by the presence of either nitric oxide (NO) or propene (C ₃H ₆). Then, a central composite design was used to study the effects of temperature and GHSV on HCN conversion, C ₃H ₆ conversion, and NO _x selectivity. On the basis of a second-order polynomial equation model, regression analysis was used to study the significance of each variable and derive equations for each response. This showed that there was a significant interaction between temperature and GHSV in HCN conversion. HCN conversion decreased at larger values of GHSV and increased at higher temperatures, up to a transition temperature that depends on the GHSV value. Temperature and gas hourly space velocity also strongly affect both C ₃H ₆ conversion and NO _x selectivity, but in these two cases, there is no significant interaction between temperature and GHSV. Contour plots of HCN conversion, C ₃H ₆ conversion, and NO _x selectivity versus temperature and GHSV were constructed from an analysis of the measured data, and these plots were then utilized to find optimum values of HCN conversion, C ₃H ₆ conversion, and NO _x selectivity over the range of conditions investigated. Conditions for optimum catalyst operation, described by high HCN conversion and low NO _x selectivity, are reported.