EFFECT OF RUTHENIUM-LOADING ON THE CATALYTIC ACTIVITY OF RU-NAZSM-5 ZEOLITES FOR NITROUS-OXIDE DECOMPOSITION

The effect of Ru-loading on the performance of Ru-NaZSM-5 catalysts pr epared by ion exchange (extent of ruthenium exchange: 20-100%) in the decomposition of nitrous oxide was studied in the temperature range of 40-700 degrees C. The turnover frequency (TOF) for nitrous oxide deco mposition (number of nitrous oxide molecules converted per ruthenium s ite per unit time) increased significantly with decreasing Ru-loading. Although lower Ru-loading resulted in higher TOF and lower apparent a ctivation energy for nitrous oxide decomposition, this occurred at the expense of stronger inhibition by oxygen. Therefore, to obtain cataly sts that remain active in the presence of excess oxygen, high Ru-loade d catalysts (close to 100% of exchange) are needed; whereas in the abs ence of oxygen, low Ru-loadings (close to 20% of exchange) are preferr ed. The high TOF observed in Ru-NaZSMS-20 was attributed to the intera ction between ruthenium and sodium cations.