Solid Acid Base Catalysts Research Articles

Simultaneous characterization of acidic and basic properties of solid catalysts by a new TPD method and their correlation to reaction rates

We propose a new TPD method for simultaneously characterizing the acidic and basic properties of solid catalysts by utilizing the co-adsorption of NH 3 and CO 2 on catalysts. First CO 2 was adsorbed on the catalyst sample; then NH 3 was adsorbed on it. Another adsorption sequence of NH 3 and CO 2, and CO 2 and NH 3 single adsorptions were also conducted. The TPD measurements were carried out by heating the catalyst sample from 373 to 773 K at a heating rate of 2.5 K min −1 in a helium stream under a total pressure of 1.3 kPa. In solid acid catalysts, there is little difference in the NH 3-TPD spectra between single and co-adsorption systems. This results from the absence of any induction effect between the acid and base sites, because the number of base sites in the solid acid catalyst is very small. In contrast, in a solid acid–base catalyst of alumina, a remarkable difference in the NH 3-TPD spectra was observed between single adsorption and co-adsorption systems. The difference in the TPD spectra between single and co-adsorption systems was ascribed to a strong induction effect appearing on the acid and base sites, which was proved by an in situ IR measurement. The validity of the TPD method was examined by correlating the number of the strong acid sites to catalytic activities of dehydrolysis of ethanol over solid acid and solid acid–base catalysts. In solid acid–base catalysts, the number of strong acid sites was calculated from the activation energy distribution for the desorption of NH 3 in a co-adsorption system because of the strong induction effect. A proportional relationship between the intrinsic reaction rate constant, which is based on the concentration of ethanol within the catalyst, and the number of strong acid sites could be obtained, regardless of the catalysts or their types or pore structure.

Enhanced product selectivity in continuous N-methylation of amino alcohols over solid acid-base catalysts with supercritical methanol.

The unique properties of supercritical fluids can be exploited for fine-tuning product selectivity. Under the conditions listed for the N-methylation of amino alcohols (see scheme) over solid acid—base bifunctional catalysts, the total yield and product selectivity could be improved. Enhanced product selectivity might be attributed to the milder reaction conditions possible with supercritical methanol, as well as the increased concentration of methanol on the catalyst.

Enhanced Product Selectivity in Continuous N‐Methylation of Amino Alcohols over Solid Acid–Base Catalysts with Supercritical Methanol

Enhanced Product Selectivity in Continuous N‐Methylation of Amino Alcohols over Solid Acid–Base Catalysts with Supercritical Methanol

Acid–base catalysis: on the example of ethylenimine production

The solid acid–base catalysts comprising of SiO 2–X m –P n –O p (X: alkali metal, alkaline earth metal) showed high catalytic activity and selectivity in vapour phase intramolecular dehydration of monoethanolamine (MEA) to ethylenimine (EI). These catalysts have acid sites and basic sites that were controlled extremely week (+4.8<H 0, H −<+9.3). On the basis of the results obtained from pulse reaction carried out with these catalysts and TPD/IR measurements of the catalysts, the following mechanism is concluded. MEA is preferentially adsorbed from the side of the hydroxyl group, which is then dissociated on acid and base sites of the catalyst simultaneously, and the consecutive dehydration occurs to form EI. The newly developed vapour phase process using these catalysts has been operated in the commercial plant since 1990.

Industrial application of solid acid–base catalysts

A statistical survey of industrial processes using solid acid–base catalysts is presented. The number of processes such as alkylation, isomerization, amination, cracking, etherification, etc., and the catalysts such as zeolites, oxides, complex oxides, phosphates, ion-exchange resins, clays, etc., are 127 and 180, respectively. The classification of the types of catalysts into solid acid, solid base, and solid acid–base bifunctional catalysts gives the numbers as 103, 10 and 14, respectively. Some significant examples are described more in detail. On the basis of the survey, the future trend of solid acid–base catalysis and the fundamental research promising for industrial success are discussed.