High-throughput screening of solid-state catalyst libraries

Combinatorial synthesis methods allow the rapid preparation and processing of large libraries of solid-state materials. The use of these methods, together.with the appropriate screening techniques, has recently led to the discovery of materials with promising superconducting(I), magnetoresistive(2), luminescent(3-5) and dielectric(6) properties. Solid-state catalysts, which play an increasingly important role in the chemical and oil industries(7), represent another class of material amenable to combinatorial synthesis. Yet typically, catalyst discovery still involves inefficient trial-and-error processes(8-10), because catalytic activity is inherently difficult to screen. In contrast to superconductivity, magnetoresistivity and dielectric properties, which can be tested by contact probes, or luminescence, which can be observed directly, the assessment of catalytic activity requires the unambiguous detection of a specific product molecule above a small catalyst site on a large library. Screening by in situ infrared thermography(11) and microprobe sampling mass spectrometry(12,13) have been suggested, but the first method, while probing activity, provides no information on reaction products, whereas the second is difficult to implement because it requires the transport of minute gas samples from each library site to the detection system. Here I describe the use of laser-induced resonance-enhanced multiphoton ionization for sensitive, selective and high-throughput screening of a library of solid-state catalysts that activate the dehydrogenation of cyclohexane to benzene. I show that benzene, the product molecule, can be selectively photoionized in the vicinity of the catalytic sites, and that the detection of the resultant photoions by an array of microelectrodes provides information on the activity of individual sites. Adaptation of this technique for the screening of other catalytic reactions and larger libraries with smaller site size seems feasible, thus opening up the possibility of exploiting combinatorial approaches as an efficient method for the discovery and optimization of solid-state catalysts.