Jörg Radnik

Combinatorial preparation and high-throughput catalytic tests of multi-component deNOx catalysts

Abstract A quaternary catalyst library of 56 samples comprising all combinations of four elements, viz. Ag, Co, Cu, In, with six equally spaced atomic fraction increments from 0 to 1 was prepared by impregnation of a proprietary mesoporous alumina support. Catalytic properties of the library were tested in the selective catalytic reduction (SCR) of NO x by propane under lean conditions in the temperature range 400–500xa0°C. The catalytic data acquired by a parallel 64-channel microreactor system with automated time-of-flight mass spectrometric analysis have been evaluated regarding selectivity–compositional relationships, synergistic effects for NO x conversion, and efficiency of propane utilization. Full conversion of NO x is achieved over Ag–Co combinations at 450xa0°C with N 2 selectivities of more than 90% and reductant utilization of 20% in a feed of 1500xa0ppm NO, 1500xa0ppm propane and 5xa0vol.% O 2 (space velocity of 36,000xa0cm 3 xa0g cat −1 xa0h −1 ). For the single-component catalysts Ag/Al 2 O 3 , Co/Al 2 O 3 , Cu/Al 2 O 3 , and In/Al 2 O 3 , the state of the elements on the mesoporous alumina was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Cobalt forms a spinel-like cobalt aluminate phase whereas copper and indium are present as oxides with small sizes not detectable by XRD. Silver occurs in both metallic state and as Ag 2 O, and forms Ag n clusters of at least two different sizes, predominantly with diameters of about 30xa0nm. The conclusions are consistent with the reducibility of the single-component catalysts samples by H 2 . Surface area measurements and pore size distributions revealed reasonable modifications of the textural properties. The main pore size of the alumina support is decreased from 7 to ca. 5xa0nm after loading of the active components.

New Insights into the Nature of Co-components and Their Impact on Pd Structure: X-ray Absorption Studies on Toluene Acetoxylation Catalysts.

Co-components are a powerful tool to tune the performance of catalysts, but their nature and their impact on the catalysts is often controversially discussed. In this study X-ray absorption spectroscopy (XAS) was employed to elucidate the nature of co-components and their impact on the catalytic reaction. In anatase-supported Pd-based catalysts for the gas-phase acetoxylation of toluene, less noble co-components (e.g., Mn, Co, and Sb) spread over the support in their oxidic form and changed their valence state on stream. Incorporated atoms such as C or a small part of the Sb affect the electronic structure of Pd. For the noble Au, only a weak interaction with the support and Pd was observed during time on stream. Only XAS at the K-edges together with investigations of the Pd L-edge for a better understanding of the electronic structure, supplemented by STEM for elemental mapping, allow such detailed insights.