ABSTRACT
Methods for the measurement of total (BET) and reduced metal (chemisorbing) surface areas in a pulse flow system have been refined and are applied to a variety of Raney® Ni and Co catalysts. The methods are quick, safe, and simple but fundamentally sound.
The more novel of the two methods uses adsorption of CO to titrate and displace H2 previously adsorbed onto the catalyst surface at 0°C or below. This avoids premature desorption (thus underestimation) of H2, measurement of excess chemically generated H2, and prior sintering of the structure, which are flaws with other H2 quantification methods when applied to Raney® catalysts.
The H2 titrated on a typical Ni catalyst amounts to the total (as opposed to only irreversible) hydrogen adsorption and thus exceeds many earlier measurements which either inadvertently or intentionally lost more weakly adsorbed quantities. The CO:H ratio, which in turn reveals CO:Ni stoichiometry, is in the 0.9-1.2 range, or about one CO molecule per surface metal atom.
The dependence of active and total surface areas on a variety of oxidizing, reducing, and thermal treatments shows more predictable behavior for Ni-based compositions than for cobalt which is apparently more complex in behavior.
