Anin situandoperandoX-ray absorption spectroscopy setup for measuring sub-monolayer model and powder catalysts

Abstract

A new spectroscopic cell has been designed for studying model catalysts using in situ or operando X-ray absorption spectroscopy. The setup allows gas treatment and can be used between 100 and 870 K. Pressures from 10(-3) Pa up to 300 kPa can be applied. Measurements on model systems in this particular pressure range are a valuable extension of the commonly used UHV characterization techniques. Using this setup, we were able to analyze the Au L3 EXAFS of a silica wafer covered with sub-monolayer concentrations of gold (0.05 ML). By modifying the sample holder, powder catalysts can also be analyzed under plug-flow conditions. As an example, the reduction of a Au/SiO2 powder catalyst prepared from HAuCl4 was followed.

Distinguishing surface adsorbed hydrogen from bulk-dissolved hydrogen in supported Pd nanoparticles using in situ Pd L3-edge XANES

“…The Pd L 3 (3175 eV) edge XANES spectra were obtained using a silicon drift detector with an energy resolution of ~130 eV. A sieve fraction of the catalyst, packed in a flow-through cell and covered by a kapton film, was placed on a heating block which can be heated to 800 K [10]. The palladium catalysts were first reduced at a ramp of 2 K/min to 423 K in 4% H 2 /He.…”

Transmission and fluorescence X-ray absorption spectroscopy cell/flow reactor for powder samples under vacuum or in reactive atmospheres

“…8 Modern flow XAS cells address the issues of fluid flow and accommodate powder samples, and in some instances the flow distribution is approximated as plug flow, which is advantageous for quantifying catalyst performance based on analysis of reaction products. 9,10 Typically, the meshed sample is pressed into the cell and held in the fluid flow path with glass/quartz wool. This design allows the fluid (usually gas) to pass uniformly through a bed of particles instead of around them.…”

“…Because the heating elements and the accompanying insulation are often bulky, most cells allowing heating and temperature control forgo fluorescence detection and allow operation only in transmission mode. 10 The cell designed by Weiher et al, 10 for example, meets most of the design criteria stated above, having the capability needed for samples under vacuum or in the presence of flowing fluids with temperature control. But it is limited to fluorescence detection and facilitates flow of reactive gases over the surface of the sample but not through a bed of particles-because the cell is designed specifically for grazing-incident XAS.…”

A high-temperature in situ cell with a large solid angle for fluorescence X-ray absorption fine structure measurement

“…Koziej et al have reported a XAFS cell for a gas-phase reaction of Pt in Pt-SnO 2 , where the sample is heated by a builtin small heater. [13][14][15] Gurlo et al have reported also another XAFS cell for research of mechanism of sensor with a small integrated heater. 16,17 Although the samples can be heated effectively keeping the large cone angle for the fluorescence XAFS using these cells, the measurements were limited to those systems with samples that could have a built-in or an integrated heater.…”

“…10 Numerous in situ fluorescence XAFS experiments have been performed on the systems of fuel cell, corrosion, catalyst, and gas sensors. 5,6,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] In situ fluorescence XAFS cells require a large fluorescence window at a position sufficiently close to the sample to secure a large solid angle. When the polymer window is used for the in situ fluorescence XAFS measurements, it is difficult to realize the large solid angle because the fluorescence window temperature raises easily even if the peripheral region of the window is cooled by water flow owing to low thermal conductivity of polymer window material.…”