Design of a high-temperature and high-pressure liquid flow cell for x-ray absorption fine structure measurements under catalytic reaction conditions

Abstract

The design and performance of a new high-pressure and high-temperature cell for measurement of x-ray absorption fine structure ͑XAFS͒ spectra of solid catalysts working in a flowing liquid are presented. The cell has flat, high-purity sintered cubic boron nitride ͑c-BN͒ windows which can tolerate high temperature ͑900 K͒ and high pressure ͑10 MPa͒. The c-BN is a new material which has the highest tensile strength, second only to diamond, and is also chemically and thermally stable. The use of the cell is demonstrated for measurements of PtPd/ Al 2 O 3 and Ni 2 P / SiO 2 hydrodesulfurization catalysts at reaction conditions. A technique called delta ͑⌬͒, involving determining the difference between XAFS spectra of the sample at reaction conditions and the bare sample, is introduced.

Nature of active sites in Ni2P hydrotreating catalysts as probed by iron substitution

“…It is assumed here that the structure of the catalyst in the working state does not change very much on quenching and that the catalyst sample referred to as spent retains its most important features. Indeed, the in situ EXAFS studies of an active Ni 2 P catalyst show that the Ni 2 P structure is retained in the bulk and that Ni-S bonds are observed on the surface [90]. The fact that the oscillations in Fig.…”

Operando QEXAFS studies of Ni2P during thiophene hydrodesulfurization: direct observation of Ni—S bond formation under reaction conditions

“…Note that ðk; tÞ has a time dependence while 1 ðkÞ, 2 ðkÞ, 3 ðkÞ are independent of time. Our previous work (Oyama et al, 2004;Kawai et al, 2006Kawai et al, , 2008Bando et al, 2009) indicated that Ni-S bond formation occurs with the Ni 2 P framework unchanged so that c 1 (t) is set constant and (1) can be reduced to…”

“…In situ X-ray absorption fine structure (XAFS) is a powerful technique for characterizing catalyst structure during reactions (Bart, 1986;Bart & Vlaic, 1987;Iwasawa, 1996); XAFS is composed of two parts: XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure). Kawai et al found a clear oscillation in the difference EXAFS spectra between a sample of Ni 2 P/SiO 2 in hydrogen before reaction and the same sample during HDS reaction that could be associated with the formation of a Ni-S bond of length 0.230 nm (Kawai et al, 2006(Kawai et al, , 2007(Kawai et al, , 2008. They also found a feature at 8333.3 eV in the XANES region that decreased in intensity in going to steady-state reaction.…”

In situ flow cell for combined X-ray absorption spectroscopy, X-ray diffraction, and mass spectrometry at high photon energies under solar thermochemical looping conditions

“…There are a large number of cells for in situ characterization by synchrotron X-ray technology. [29][30][31][32][33][34][35][36][37][38][39][40] Most cells are FIG. 1.…”