Nanocatalysts based on palladium(II), copper(II) and acid-modified vermiculite compounds for the oxidation of carbon monoxide with atmospheric oxygen

In this work, the physicochemical properties of natural vermiculite, its acid-modified forms, and copper–palladium catalysts based on it were investigated. Acid-modified forms of vermiculite were obtained by refluxing with nitric acid solutions (0.25; 0.5; 1.0; 3.0; 4.0; 6.0; and 8.0 mol/L) for one hour. Nanocatalysts were prepared by the impregnation method at moisture capacity, followed by drying at 1000C for 3 hours. The initial vermiculite, the acid-modified samples, and the catalysts were characterized by X-ray phase analysis, IR spectroscopy, and nitrogen adsorption. Catalyst samples were tested in the reaction of carbon monoxide oxidation with oxygen under the following conditions: initial concentration of 300 mg/m3, temperature of 200C, relative humidity of the gas–air mixture of 67%, and volumetric flow rate of 1 L/min. It was established that the natural material is polyphase and, in addition to the main vermiculite phase (52 wt.%), contains impurity phases of muscovite, cordierite, and sepiolite, each with a content not exceeding 14–18 wt.%. The deposited palladium(II) and copper(II) compounds were well homogenized on the surface of the carrier and did not undergo phase transformations. The crystallites of the vermiculite phase were nanosized. IR spectroscopy showed that under the action of nitric acid (CHNO3>4 mol/L) and upon fixation of palladium(II) and copper(II) compounds, the layered structure of vermiculite was altered, its amorphization increased, and nanosilica was formed. As a result of acid modification, the specific surface area of vermiculite samples increased from 4.49 m2/g to 282.0 m2/g. Testing of the nanocatalyst samples showed that CO oxidation occurred in a stationary mode only when the carrier had been modified at CHNO3>4 mol/L, with the degree of carbon monoxide conversion reaching 88%.