Offline    1.412.963.6385

Build My System

Notes

METAL CRYSTALLITE SIZE DETERMINATION: COMPARISON OF CHEMICAL AND PHYSICAL METHODS

Recent Altamira Notes have discussed the use of several different chemisorption techniques to determine crystallite sizes for supported metal catalysts.These techniques, temperature-programmed desorption, static chemisorption, and pulse chemisorption, can all be described as "chemical" methods because they rely on some way of monitoring the chemisorption or desorption of molecules on metal surfaces. A second general approach to the determination of metal crystallite sizes involves the use of techniques which may be described as "physical" methods. The objective of this Note is to compare the chemical methods described in earlier Notes to several physical methods discussed below.

PULSE CHEMISORPTION

Previous issues of Altamira Notes have discussed different selective chemisorption techniques and how they may be used to determine the specific metal surface area of supported metal catalysts.   One additional technique commonly used for the same purpose is pulse chemisorption. This method is one of the simplest, most straightforward ways to measure adsorbate uptake by a metal surface; however, as with most other measurements in catalysis, interpretation of the results can be problematic if the nature of the catalyst system and the experiment itself are not well-understood. This Altamira Note discusses the principles of pulse chemisorption experiments as well as some common experimental observations

VOLUMETRIC CHEMISORPTION METHODS FOR METAL CRYSTALLITE SIZE DETERMINATION

One of the most important properties which characterizes a supported metal catalyst is its specific metal surface area. This information may be gained by a number of different experimental techniques (1, 2) and is usually reported as the average metal crystallite diameter of the catalyst. This parameter provides a means of comparing catalysts prepared by different methods or in different laboratories. A previous Altamira Note (September 1989) discussed how surface area measurements may be obtained from temperature-programmed desorption data for supported metal catalysts. This Note will focus on how the same information is obtained from a more traditional chemisorption method known as volumetric or static chemisorption