An overview is given of the selective catalytic reduction of NO x by ammonia (NH 3 -SCR) over metal-exchanged zeolites. The review gives a comprehensive overview of NH 3 -SCR chemistry, including undesired side-reactions and aspects of the reaction mechanism over zeolites and the active sites involved. The review attempts to correlate catalyst activity and stability with the preparation method, the exchange metal, the exchange degree, and the zeolite topology. A comparison of Fe-ZSM-5 catalysts prepared by different methods and research groups shows that the preparation method is not a decisive factor in determining catalytic activity. It seems that decreased turnover frequency (TOF) is an oft-neglected effect of increasing Fe content, and this oversight may have led to the mistaken conclusion that certain production methods produce highly active catalysts. The available data indicate that both isolated and bridged iron species participate in the NH 3 -SCR reaction over Fe-ZSM-5, with isolated species being the most active.

Standing out from the vast majority of metal organic coordination polymers is the class of highly porous basic zinc carboxylates developed by Yaghi and co-workers.[1] Its prototype is MOF-5 (MOF = metal organic framework), in which {Zn 4 O} building blocks are linked together by terephthalate bridges to form a zeolite-like, cubic framework.[2] The extremely high specific surface area [2] of up to 4500 m 2 g À1 and a pore volume of 0.69 cm 3 cm À3 (for MOF-177), which has not been surpassed by any other crystalline substance, and thermal stability (up to 350 8C) opens up fascinating perspectives for the supramolecular host-guest chemistry.[3] Applications for these materials in miniaturized fuel cells and convenient gas-storage devices (for H 2 , CH 4 ), as gas sensors and for gas separation, as catalyst materials, and also for molecular electronics are emerging. [4] A report on the quantitative inclusion of C 60 and large polycyclic dye molecules (e.g. Astrazon Orange R) into the cavities of MOF-177 single crystals attracted our attention. [5] Could these MOF host lattices also be suitable to efficiently and selectively absorb typical metal organic chemical vapor deposition (CVD) precursors, provided these were volatile (gas absorption) or very soluble in nonpolar hydrocarbons and had matching size and shape to fit into the cavity? The release of the metal atoms of the precursors imbedded in the

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