http://www1.udel.edu/chem/polenova/PDF/Polyoxometalates/POMs_Catalysis_NMR_ChemRev1998.pdf

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

In the last few years there has been a rapid growth in governmental funding and research activities worldwide for CO2 capture, storage and utilization (CSU), due to increasing awareness of the link between CO2 accumulation in the atmosphere and global warming. Among the various technologies and processes that have been developed and are emerging for CSU of CO2, solid CO2-adsorbents are widely applied. In this review, these solid CO2-adsorbents are classified into three types according to their sorption/desorption temperatures: low-, intermediate- and high-temperature adsorbents with temperatures ranging from below 200 °C, between 200–400 °C and above 400 °C, respectively. For each type of solid CO2-adsorbent, the synthesis, interaction mechanism with CO2 and sorption performance, potential applications and problems are reviewed. In the last section, several representative CO2-sorption-enhanced catalytic reactions are discussed. It is expected that this review will not only summarize the main research activities in this area, but also find possible links between fundamental studies and industrial applications.

CO2 capture by solid adsorbents and their applications: current status and new trends

Publisher Summary This chapter describes the essence of the catalytic chemistry of heteropoly compounds in solution and in the solid state. The catalytic properties of heteropoly compounds have drawn wide attention, owing to the versatility of these compounds as catalysts, which has been demonstrated both by successhl large-scale applications and by promising laboratory results. Heteropolyanions are polymeric oxoanions formed by condensation of more than two different mononuclear oxoanions. Heteropolyanions formed from one kind of polyanion are called isopolyanions. Acidic elements such as Mo, W, V, Nb and Ta, which are present as oxoanions in aqueous solution, tend to polymerize by dehydration at low pH, forming polyanions and water.Heteropoly catalysts can be applied in various ways. They are used as acid as well as oxidation catalysts. They are used in various phases, as homogeneous liquids, in two-phase liquids (in phase-transfer catalysis), and in liquid-solid and in gas-solid combinations, etc.

Catalytic Chemistry of Heteropoly Compounds

Heteropolyanions are polymeric oxoanions which are formed by the condensation of more than two different oxoanions [Eq. (1)l. Polyanions consisting of one kind of oxoanion are called isopolyanions [Eq. (2)]. Acidic elements such as Mo, W, V, Nb, and Ta are present as oxoanions in aqueous solutions and polymerize to form polyanions at low pH. Free acids (or acid forms) of these species are called heteropoly and isopoly acids, respectively. Here, the term “heteropoly compounds” is used for heteropoly acids and their salts.

Heterogeneous catalysis by heteropoly compounds of molybdenum and tungsten

Syntheses of new porous frameworks with specific pore size and type are of considerable interest for the appearance of zeolite-like functionalities. It is useful to take advantage of metal complex-assembled compounds because of designable frameworks, high microporosity, and flexible frameworks based on a variety of coordination geometries of metal centers and multifunctionality of bridging organic parts. Many recent reports show that the synthesis procedures are developing from serendipitious to rational level. Therefore, the micropore chemistry of metal complex-based assemblages is directed toward not only new frameworks but also functionalities such as gas and small molecule adsorption, ion exchange, heterogeneous catalysis, photo-chemical and -physical properties. For chemical and physical functionalities robustness of a framework is required even in the absence of guest molecules in the cavity. The stability is largely dependent on the structural dimensionality of the assemblages. A wide variety of st...

Functional Micropore Chemistry of Crystalline Metal Complex-Assembled Compounds

Physical adsorption of gases at high pressure. IV. An improvement of the Dubinin—Astakhov adsorption equation

Physical adsorption of gases at high pressure: V. An Extension of a Generalized Adsorption Equation to Systems with Polar Adsorbents

Isotherms and IR spectra were measured for CO2-MZSM-5 (M = Li+, Na+, K+, Rb+, Cs+) adsorption systems. The observed adsorption characteristics were well approximated by a physical adsorption where the van der Waals force and an electrostatic interaction force are operating: the degree of irreversible adsorption (chemisorption) was less than 10% of the total adsorption. Although the adsorbed CO2 molecule interacts with both the cation and the pore wall, only the CO2-cation interaction can convert the IR inactive ν1 vibration into an IR active state. The adsorption model proposed enables us to calculate the initial heat of adsorption as well as the molecular orientation angle of CO2 against the cation site.

Adsorption of CO2 over univalent cation-exchanged ZSM-5 zeolites

Infrared spectra of methane adsorbed by ion-exchanged ZSM-5 zeolites

Amounts of nitrogen adsorbed by ion-exchanged ZSM-5 zeolites (H+, Li+, Na+, K+, Rb+, and Cs+) and silicalite have been measured under various conditions; pressure=6.7×102–6.7×104 Pa, temperature=196–273 K. IR spectra of adsorbed nitrogen have also been measured at 226 K under various nitrogen pressures (1.3×102–4.0×104 Pa). The adsorption capacity, the specific surface area, and the heat of adsorption have been evaluated from the adsorption data. These quantities coupled with the IR peak shifts observed have revealed that the nitrogen molecule adsorbed on a small and strong cationic site (Li+, Na+) has an orientation in which the longer molecular axis lies in parallel with the direction of the electric field of the cation site. It has also been revealed that the nitrogen molecule adsorbed on a large (K+, Rb+, Cs+) or weak (H+) cationic site takes on no special orientation. The electric field evaluated by analyzing the IR intensity is consistent with the adsorption model obtained.

Yoshisada Ogino

Papers

Physical adsorption of gases at high pressure. IV. An improvement of the Dubinin—Astakhov adsorption equation

Physical adsorption of gases at high pressure: V. An Extension of a Generalized Adsorption Equation to Systems with Polar Adsorbents

Adsorption of CO2 over univalent cation-exchanged ZSM-5 zeolites

Infrared spectra of methane adsorbed by ion-exchanged ZSM-5 zeolites

Infrared spectra of nitrogen adsorbed on ion-exchanged ZSM-5 zeolite.