In situ X-ray absorption spectroscopy

The reaction on the catalyst surface was followed by in situ i.r. spectroscopy using a Bruker IFS88 FTIR spectrometer for the characterisation of sorbed species and mass spectroscopy for the analysis of gas phase. The state of Pt was further investigated by in situ X-ray absorption spectroscopy (Daresbury, UK, beamline 9.1, transmission mode, Si(220) monochromator, Pt-Lj, edge). Details of catalyst characterisation techniques are reported elsewhere [13,14]. 

However, it should be noted that the structure of those bimetallic particles (Ag-In) can be changed under the conditions of the catalytic reaction, that is, in presence of the reactants, as recently shown by in situ X-ray absorption spectroscopy of acrolein hydrogenation [100]. 

There have been many recent studies in support of this mechanistic approach. Stepwise reductive formation of Ag3+ and Ag4+ clusters has been followed using spectroscopic methods by Henglein [33], Reduction of copper (II) to colloidal Cu protected by cationic surfactants (NR4+) through the intermediate Cu+ prior to nucleation of the particles [36] as monitored by in situ x-ray absorption spectroscopy is another example. The seed-mediated synthesis also serves as evidence in support of this mechanism [38-41],... 

Grunwaldt J-D, Baiker A. Axial variation of the oxidation state of Pt-Rh/Al203 during partial methane oxidation in a fixed-bed reactor an in situ X-ray absorption spectroscopy study. Catal Lett. 2005 99 5. 

Ressler T, Hagelstein M, Hatje U, Metz W. In situ X-ray absorption spectroscopy studies on chemical oscillations in the C0/02 system on supported Pd catalysts. J Phys Chem B. 1997 101 6680. 

Grunwaldt J-D, Ramin M, Rohr M, Michailowski A, Patzke GR, Baiker A. High pressure in situ x-ray absorption spectroscopy cell for studying simultaneously the liquid phase and the solid/liquid interface. Rev Sci Instrum. 2005 76 054104. 

The use of synchrotron based in situ x-ray absorption spectroscopy (XAS) for the study of catalysis, both heterogeneous and electrocatalysis has matured over the last decade with simultaneous efforts in the United Sates, European Union and Japan. Some recent exemplification of the state of the art can be obtained in the following references, " and an extensive database of literature on its application to catalysis can be accessed electronically (www.exafs.chem.msu.su/ papers). Detailed aspects on application of the technique and methodology used for data analysis has been recently published. " ... 

Mukerjee, S. In-situ x-ray absorption spectroscopy of carbon-supported Pt and Pt-alloy electrocatalysts correlation of electrocatalytic activity with particle size and alloying, Wiley VCH, 2003. 

In-Situ X-Ray Absorption Spectroscopy of Carbon-Supported Pt and Pt-Alloy Electrocatalysts Correlation of Electrocatalytic Activity with Particle Size and Alloying... 

A. Tadjeddine, D. Guay, M. Ladouceur, G. Tourillon, Electronic and structural characterization of underpotentially deposited submonolayers and monolayer of copper on gold (111) studied by in situ X-ray-absorption spectroscopy. Phys. Rev. Lett. 66, 2235-2238, 1991. 

In this endeavor synchrotron spectroscopy has played an important role in understanding the effect of fundamental parameters such as electronic density of states and short-range atomic order. The primary advantages of using the synchrotron are (1) the ability to probe these parameters in situ while the interface is under electrochemical control and (2) the fact that these can be measured with element specificity. The latter is particularly useful when investigating multi-component alloy clusters. In addition, this technique lends itself to systems with limited long-range order, which is typical for these nanoclusters used in fuel-cell electrode interface. This chapter describes some recent results with in-situ X-ray absorption spectroscopy, which has provided a direct probe into the variations of the Pt i/-band vacancy (normalized with respect to number of surface atoms) between... 

Bare, S.R., Yang, N., Kelly, S.D. and Mickelson, G.E. (2007) Design and operation of a high pressure reaction cell for in situ X-ray absorption spectroscopy. Catal. Today, 126, 18-26. 

Ressler, T. (2003). Application of time-resolved in-situ x-ray absorption spectroscopy in solid-state chemistry. Anal. Bioanal. Chem. 376, 584-593. 

The existence of very small particles was indeed evidenced using in situ X-ray absorption spectroscopy (XAS) (Walker et al. 1990) which showed that in the active catalyst CeH2+x—Ru the ruthenium particles were a mixture of approximately 3.5 nm crystallites and very low coordination clusters while the inactive catalyst Ce02-Ru contained essentially bulk metallic ruthenium. 

Several techniques can be used to measure the extent of reduction. TPR, oxygen titration and in situ X-ray absorption spectroscopy are techniques that are able to give information on the fraction of reduced cobalt. However, the measurements are fundamentally different and, indeed, they often give different results. This work deals with a comparison of results obtained from these methods in order to verify the reliability of the techniques. Five supports have been examined Si02, Ti02, a-Al203, and two Y-AI2O3 supports. 

Platinum and palladium are effective catalysts for alcohol oxidation when used alone however, significant stability and selectivity improvements have been observed on incorporation of a second (usually less active) metal promoter such as Bi, Pb, and Sn [63-65]. These observations are common to aerobic selox of allyhc and benzylic alcohols, as well as polyols such as propylene glycol [64] and glycerol [66]. In the case of Bi, in situ X-ray absorption spectroscopy (XAS) and attenuated total reflection infrared spectroscopy (ATR-IR) indicate that the promoter protects Pt against deactivation by overoxidation and prevents site blocking by, for example, aromatic solvents [67]. 

Chang, J. K., M. T. Lee, W. T. Tsai, M. J. Deng, and I. W. Sun. 2009. X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy studies on reversible insertion/desertion of dicyanamide anions into/from manganese oxide in ionic liquid. Chemistry of Materials 21 2688-2695. 

Miedema PS, Schooneveld M, Bogerd R, Rocha T, Havecker M, Gericke A, Groot F (2011) Oxygen binding to cobalt and iron phthalocyanines as determined from in situ X-ray absorption spectroscopy. J Phys Chem C 115(51) 25422-25428... 

While much of the work in the literature has speciflated on the presence of neutral Au clusters, there has been very little in-situ experimental evidence to support these ideas. Calla and Davis claerly showed the presence and the activity of neutral Au clusters under reaction conditions. They followed the CO oxidation reaction over Au supported on AI2O3 using in-situ X-ray absorption spectroscopy as well as with transient isotopic labeling studies. Their results indicate that Au + is reduced during calcination and that the active species throughout the reaction appears to be metallic Au . 

Noninvasive in situ analysis of the state of the catalysts became rather popular in the last decade, in particular using X-ray absorption spectroscopy methods (Grunwaldt and Baiker, 2005 Grunwaldt et al., 2006 Flannemann et al., 2007). For instance, Grunwaldt et al. studied CPOX of methane over Rh and Pt—Rh using in situ X-ray absorption spectroscopy in an in situ spectroscopic cell (Hannemann et al., 2007). The measurements were performed at a synchrotron. However, spatial analysis of the catalyst is beyond the scope of this chapter that focusses on the analysis of the gas phase in a catalytic stmcture. 

Mukerjee S, McBreen J. An in situ X-ray absorption spectroscopy investigation of the effect of Sn additions to carbon-supported Pt electrocatalysts Part 1. J Electrochem Soc 1999 146 600-6. 

Russell AE, Maniguet S, Mathew RJ, Yao J, Roberts MA, Thompsett D. In situ X-ray absorption spectroscopy and X-ray diffraction of fuel cell electrocatalysts. J Power Sources 2001 96 226-32. 

Croze, V, Ettingshausen, F., Melke, I, Soehn, M., Stuermer, D. and Roth, Ch., The use of in situ X-ray absorption spectroscopy in apphed fuel ceU research . Jb raaZ of Applied Electrochemistry 40, 877-883 (2010). 

Ramaker, D. E., Gatewood, D., Korovma, A., Garsany, Y., and Swider-Lyons, K. E. 2010. Resolving sulfur oxidation and removal from Pt and PtjCo electrocatalysts using in situ x-ray absorption spectroscopy. lournal of Physical Chemistry C 114 11886-11897. 

---