Fractional Factorial Study of HCN Removal over a 0.5% Pt/Al2O3 Catalyst: Effects of Temperature, Gas Flow Rate, and Reactant Partial Pressure

Hydrogen cyanide (HCN) oxidation under lean conditions was studied on 0.5% Pt/Al2O3 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 (C3H6). Then, a central composite design was used to study the effects of temperature and GHSV on HCN conversion, C3H6 conversion, and NOx selectivity. On the basis of a secondorder 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 C3H6 conversion and NOx selectivity, but in these two cases, there is no significant interaction between temperature and GHSV. Contour plots of HCN conversion, C3H6 conversion, and NOx 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, C3H6 conversion, and NOx selectivity over the range of conditions investigated. Conditions for optimum catalyst operation, described by high HCN conversion and low NOx selectivity, are reported.