Detection limits and artifacts in x-ray microanalysis of industrial catalysts

High resolution analytical electron microscopy technique have been applied to catalysts characterization since recently. Because the low concentrations and high dispersion of the active phases in most of industrial catalysts, the detection of individual phases is rather difficult. Among other factors, poor signals arising from either small metal particles or intermediate phases are common, which makes it that analytical techniques, i.e. energy dispersive spectrometry, is used in conditions close to the detection limits. For example, typical 50 nm-thick-support areas, with a small metal particle of about 4nm diameter on it, should represent a volume of matter of about 10-17g and 10-19g respectively. According to theoretical calculations the minimal mass fraction (MMF) for a 5 nm - electron-probe-diameter should be about 0.7%. Also, cautionary guidelines to avoid secondary X-ray fluorescence must be followed. In particular, a very small beam diameter focused on a thin area should lead to a spatial resolution level of about 5 nm, between distinct phases in a catalyst