Materials and Pressure Gap

Assmann J, Narkhede V, Bteuer A, Muhler M, Seitsonen AP, Knapp M, Crihan D, Farkas A, Mellau G, Over H. 2003. Heterogeneous oxidation catalysis on mthenium Bridging the pressure and materials gaps and beyond. J Phys Cond Matt 20 184017. 

Like most surface science techniques, conventional in situ STM studies have been carried out in UHV on model catalysts consisting of extended planar surfaces. When extrapolating the information obtained in UHV surface science studies to real-world catalysis, two issues have generally concerned the catalysis community, namely, the pressure and material gaps. 

As mentioned above, most modem surface-sensitive techniques operate under vacuum, and are often used for studies in model systems. Nevertheless, there have been recent attempts to extend that work to more relevant catalytic problems. Great advances have already been made to bridge the so-called pressure and materials gaps, that is, to address the issues related to the differences in catalytic behavior between small simple samples (often single crystals) in vacuum, and supported catalysts under higher (atmospheric) pressures [155-157], Nevertheless, more work is still needed. 

The nano-architecture is thus an important aspect to consider for the design of novel catalysts and a critical element to consider also in analyzing how to bridge the gap between model and real catalysts. In fact, in addition to the issues of pressure and material gap , the complexity gap exists." Goodman " over ten years ago pointed out that despite the successes in modelling catalysts with single crystals, there is a clear need to develop models with higher levels of complexity and which take into account the 3D nanoarchitecture. 

Freund, H.J., Kuhlenbeck, H., Libuda, J., Rupprechter, G., Baumer, M., Hamann, H. (2001) Bridging the pressure and materials gaps between catalysis and surface science clean and modified oxide surfaces. Top. Catal, 15, 201. 

Bron M, Teschner D, Knop-Gericke A, Steinhauer B, Scheybal A, Havecker M, Wang D, Fodisch R, Honicke D, Wootsch A, Schlogl R, Claus P. Bridging the pressure and materials gap in-depth characterisation and reaction studies of silver-catalysed acrolein hydrogenation. Journal of Catalysis. 2005 234(l) 37-47. 

Dellwig T, Rupprechter G, Unterhalt H, Freund H-J (2000) Bridging the pressure and materials gaps High pressure sum frequency generation study on supported Pd nanoparticles. Phys Rev Lett 85 776... 

In recent years, considerable efforts have been made in a variety of research groups to bridge the pressure and material gap and to experimentally as well as theoretically establish the new methods required to continuously vary the conditions starting form the model catalyst side (bottom up approach) or form the real catalyst side (top down approach). First examples support the importance of a detailed understanding of environmental and material complexity effects on catalytic reactions. The common distinction of pressure gap and material gap as depicted in Fig. 1.54 might, however, also be oversimplified as has been demonstrated in a recent contribution on the oxidation of CO on a ruthenium surface. The first step in this reaction consists in an... 

This chapter proceeds with a general discussion of the overall catalytic cycle and Sabatier s principle in order to illustrate the comparison of relative kinetic and thermodynamic steps in the overall cycle. This is followed by a fundamental discussion of the intrinsic surface chemistry and the application of transition state theory to the description of the surface reactivity. We discuss the important problem of the pressure and material gap in relating intrinsic rates with overall catalytic behavior and then describe the influence of the tatic reaction environment including promoters, cluster size, support, defects, ensemble, coadsorption and stereochemistry. Lastly, we discuss the transient changes to the surface structure as well as intermediates and their influence on catalytic performance. 

---