Chemisorption of carbon monoxide on metal surfaces by pulse chromatography

Abstract

A pulse chromatographic procedure has been developed for the measurement of the surface areas of catalytic metals by carbon monoxide chemisorption. This procedure consists of repeated injection of carbon monoxide pulses into a helium carrier gas passed over the metal surface to establish the cumulative saturation value which corresponds to irreversible chemisorption. Independent measurements made on unsupported platinum and nickel metal powders with volumetric and chromatographic surface area procedures and on supported nickel catalysts with a volumetric chemisorption procedure have established the validity of the pulse chromatographic procedure for determination of carbon monoxide chemisorption. Advantages of the pulse chromatographic procedure include the avoidance of high vacuum procedures and the avoidance of corrections for reversible physical adsorption.GAS CHEMISORPTION is an established technique commonly used for the estimation of the accessible reactive surface of metal catalysts. The gases most commonly used are hydrogen and carbon monoxide. This technique is applicable to a variety of metal catalysts which include the transition metals (iron, nickel, cobalt, and the platinum family). Volumetric gas adsorption procedures are most commonly used for chemisorption measurement. However, several recent applications have been made of chromatographic procedures (1-6).Chromatographic measurements have several attractive aspects which include:1. High vacuum procedures are avoided. 2.Measurements are made under dynamic flow conditions approximating those under which catalysts are most commonly used. In the present study, a pulse chromatographic procedure has been used to measure the chemisorption of carbon monoxide on supported nickel and unsupported nickel and platinum catalysts. This chemisorption procedure consists of repeated exposure of the catalysts to carbon monoxide pulses to establish the cumulative saturation value which corresponds to irreversible adsorption at room temperature. A comparison is made with results from measurements made with the classical volumetric procedure to establish the equivalence of the gas chemisorption values determined by the two procedures on the 1

Hydrodechlorination of Carbon Tetrachloride to Chloroform in the Liquid Phase with Metal-Supported Catalysts. Effect of the Catalyst Components

“…The number of exposed metal atoms (Me s , atom g -1 ) on the catalysts was determined by CO chemisorption using a dynamic pulse technique . Samples of 0,5 g were evacuated under an Ar flow of 30 cm 3 min -1 at 573 K for 2 h. After the samples cooled at 298 K, pulses of CO (50 μL) were introduced into the argon stream until saturation of the sample was obtained.…”

N2O Pulse Titration of Ni/α-Al2O3 Catalysts: A New Technique Applicable to Nickel Surface-Area Determination of Nickel-Based Catalysts

“…Many researchers have also investigated the static-volumetric and dynamic chemisorption methods to measure the surface area of nickel on nickel-based catalysts in the following manner: (i) probe gas molecules, such as H 2 − and CO, , are adsorbed on nickel-based catalysts, (ii) the number of surface nickel atoms is calculated from the adsorbed amount of the molecules and the stoichiometry between nickel and chemisorbed gas molecule, and then (iii) the number of surface nickel atoms thus calculated is converted to the nickel surface area using the area occupied by one surface nickel atom. , With a static-volumetric chemisorption method the amount of the gas adsorbed at constant temperature is given as a function of the equilibrium pressure (adsorption isotherm). The apparatus for this method is equipped with an appropriative vacuum device.…”

Applications of Gas Chromatography in Catalysis

“…By the application of the above technique, correction for reversible physical adsorption can be avoided. Good agreement between volumetric and pulse chromatographic procedures has been observed (Brooks and Kehrer, 1969) by independent measurement on unsupported platinum and nickel metal powders, and on supported nickel catalyst for the determination of carbon monoxide chemisorption.…”

“…Recently, Brooks and Kehrer (1969) have developed a pulse chromatographic procedure for the measurement of the surface areas of catalytic metals by carbon monoxide chemisorp- tion. In this method, exposure of the catalyst to carbon monoxide pulses is repeated until the cumulative saturation value, corresponding to irreversible adsorption at a particular temperature, is established.…”