Damodara M. Poojary

Applications of Combinatorial Methods in Catalysis

With rising economic demands for higher efficiency and productivity in research and development, combinatorial catalysis is increasingly being implemented to bring more catalysts per unit time to the marketplace. High-throughput automated synthesis and advanced screening technologies are now being applied to the discovery of more efficient homogeneous as well as heterogeneous catalysts and materials. The combinatorial process allows the exploration of large and diverse compositional and parameter spaces by establishing an integrated workflow of rapid parallel or combinatorial synthesis of large numbers of catalytic materials, subsequent high-throughput assaying of these compounds and large-scale data analysis. The number of experiments that can be screened has risen by orders of magnitude resulting in a much higher probability of discovering new catalysts or materials. The goal of this review is to provide an overview of selected advances that have been made in this rapidly growing field in both academia and industry over the past several years.

X-ray powder structure of Sr2CeO4: A new luminescent material discovered by combinatorial chemistry

Abstract A new luminescent inorganic oxide with the composition Sr 2 CeO 4 has been discovered using combinatorial chemical methodologies. A combinatorial library consisting of more than 25u2008000 chemically distinct compositions was prepared by an automated thin film physical vapor deposition method. The lead compound responsible for the luminescence in the Sr–Ce–O region of the library was prepared in bulk quantity for structural investigation. The three-dimensional structure of the compound was solved ab initio from X-ray powder diffraction data and refined by the Rietveld method. The structure consists of one-dimensional chains of edge-sharing CeO 6 octahedra that are linked together by Sr 2+ ions. A bulk sample prepared with the same elemental composition as above but heated for a shorter time was analyzed for the presence and amount of different phases formed in the initial stages of the reaction. The results show that this sample consists of SrCO 3 , CeO 2 , SrCeO 3 , and Sr 2 CeO 4 . Upon prolonged heating the former three phases convert to the final product, Sr 2 CeO 4 .

Application of Combinatorial Catalysis for the Direct Amination of Benzene to Aniline

Abstract High-throughput synthesis and screening methods have been developed for the direct amination of benzene to aniline using solid cataloreactants as oxidants. The discovery libraries consisted of hundreds of samples in the primary screen, and arrays of 24 catalysts in the secondary screen. Catalysts were prepared in multi-well batch reactors and screened in parallel for catalytic activity using modified TLC detection and fast serial GC detection as primary screen and secondary screen, respectively. Around 25,000 samples were screened in about a year. Promising hits identified in the high-throughput screens were successfully scaled up and optimized in conventional autoclaves. Novel cataloreactant systems consisting primarily of a noble metal and a reducible metal oxide have been discovered. An optimized cataloreactant, Rh/Ni-Mn/K-TiO2 achieved a stable 10% benzene conversion and >95% selectivity to aniline at 300xa0°C and 300xa0bar for a reaction time of about 2xa0h. Significantly, the cataloxidant can be regenerated repeatedly without a substantial loss of performance by reoxidation in air.

Kombinatorische Parallelsynthese und Hochgeschwindigkeitsrasterung von Heterogenkatalysator-Bibliotheken

Weniger als eine Minute war notig, um die katalytische Aktivitat und die Selektivitat eines Elements in einer kombinatorischen Bibliothek aus ternaren Rh-Pd-Pt-Cu-Legierungen zu bestimmen. Damit genugten zwei Stunden fast, um eine Bibliothek aus 136 Elementen zu uberprufen. Die Bibliotheken enthielten die Elemente (ca. 2–4 μg Material jeweils) in zweidimensionaler Anordnung und wurden mit Dunnschichttechniken synthetisiert. Zur Analyse wurden sie unter Einsatz von Rastertechniken, die mit Massenspektrometrie gekoppelt waren (siehe Bild), vermessen.

Application of combinatorial catalysis for the direct amination of benzene to aniline

Abstract High-throughput synthesis and screening methods have been developed for the direct amination of benzene to aniline using solid cataloreactants as oxidants. The discovery libraries consisted of hundreds of samples in the primary screen, and arrays of 24 catalysts in the secondary screen. Catalysts were prepared in multi-well batch reactors and screened in parallel for catalytic activity using modified TLC detection as a primary screen and fast serial GC detection as a secondary screen. Around 25,000 samples were screened in about a year. Promising hits identified in the high-throughput screens were successfully scaled up and optimized in conventional autoclaves. Novel cataloreactant systems consisting primarily of a noble metal and a reducible metal oxide have been discovered. Rh, Ir, Pd, and Ru were found to be suitable noble metal dopants. Ni and Co oxides were the only active and selective oxidants identified. Ni is the most active oxidant but requires a Mn dopant as a stabilizer to improve the regenerability, whereas Co is stable even at high regeneration temperatures. The best performing cataloreactants contain Rh or Ir as noble metals, NiO as an oxidant, and ZrO 2 or K–TiO 2 as carrier. An optimized cataloreactant, Rh/Ni–Mn/K–TiO 2 achieved stable 10% benzene conversion and >95% selectivity to aniline at 300xa0°C and 300xa0bar. Significantly, the cataloxidant can be regenerated repeatedly without a substantial loss of performance by reoxidation in air. Any noble metal oxides formed during regeneration are effectively reduced in situ during the next amination reaction.

Selective oxidation of alcohols by combinatorial catalysis

Abstract High-throughput synthesis and screening of polyoxometalate (POM) and supported-metal libraries have been developed for the selective aerobic oxidation of alcohols to the corresponding aldehydes/ketones in the liquid phase. Libraries consisting of 96 catalysts were prepared in multi-well reactors and screened for catalytic activity using TLC, GC and NMR detection methods. Promising hits identified in the high-throughput primary screens were successfully scaled up and optimized in conventional laboratory test units. Isolated yields confirm high selectivities of more than 90% with quantitative conversions. Substrates tested include primary and secondary alcohols. Specific results will be presented for hydroxymethyl-substituted heterocycles and bicyclo-octanols.