REACTION STUDIES OF THE SELECTIVE REDUCTION OF NO BY VARIOUS HYDROCARBONS

A number of factors affecting the behavior of ZSM-5 and Ferrierite zeo lites have been studied and implications concerning mechanism have bee n deduced. Increasing the loading of the ZSM-5 with Co2+ is shown to i ncrease both the selective catalytic reduction (SCR) of NO and hydroca rbon combustion activities, but not to alter the selectivity under a g iven set of reaction conditions. The latter was nearly constant at all temperatures and valued at unity up to 673 K, where it precipitously fell at higher temperature. Selectivity was also a function of space v elocity and of the NO/C4H10 ratio. Both SCR and combustion followed si milar patterns with different charge balancing cations (including H) w ith a few notable exceptions. The shifts in temperature required to ob tain a given conversion of NO to N-2 were relatively minor compared wi th those required for constant combustion. NO and NO2 were equivalent in SCR in the presence of excess O-2. In the absence of O-2, NO2 was t he better oxidant at low temperature although NO became quite effectiv e above 800 K. The tabulated data at various temperatures showed a str ong molecular sieve effect in the SCR reaction when neononane was empl oyed, but not for the combustion reaction. None of the other molecules employed showed this behavior. Plots of conversion of NO to N-2 vs co nversion of hydrocarbon to CO2 correlated the data for all hydrocarbon s, regardless of size, on single curves, except for neononane over Co- and CH4 over CuZSM-5. Even HZSM-5 behaved in this way. A further inte resting molecular sieve effect was found when reactions over CoFer (Fe rrierite) were compared with those over CuZSM-5. (C) 1994 Academic Pre ss, Inc.