UV−Vis Spectroscopy of Iodine Adsorbed on Alkali-Metal-Modified Zeolite Catalysts for Addition of Carbon Dioxide to Ethylene Oxide

Abstract

The basicity of alkali-metal-exchanged (Na, K, Cs) zeolites X and Y was probed by UV−vis diffuse reflectance spectroscopy of adsorbed iodine. The observed blue shift in the visible absorption spectrum of adsorbed iodine, compared to gaseous iodine, correlated well with the negative charge on the framework oxygen atoms calculated from the Sanderson electronegativity equalization principle. The blue shifts associated with iodine adsorbed on classical catalytic supports like silica, alumina, and magnesia suggest that the iodine adsorption technique for probing basicity is applicable to a wide variety of solids. Iodine was also adsorbed on X and Y zeolites containing occluded cesium oxide formed by decomposition of impregnated cesium acetate. However, the iodine appeared to irreversibly react on these strongly basic samples, possibly forming an adsorbed triiodide ion. As a complement to the adsorption studies, the activity of alkali-metal-containing zeolites for the base-catalyzed formation of ethylene carbonate from ethylene oxide and carbon dioxide was investigated. Among the ion-exchanged zeolites, the cesium form of zeolite X exhibited the highest activity for ethylene carbonate formation. The catalytic activity of a zeolite containing occluded cesium was even higher than that of a cesium-exchanged zeolite. The presence of water adsorbed in zeolite pores promoted the rate of ethylene carbonate formation for both cesium-exchanged and cesium-impregnated zeolite X.

Synthesis of Propylene Carbonate from Carbon Dioxide and Propylene Oxide Using Zn-Mg-Al Composite Oxide as High-efficiency Catalyst

“…It is also noted that the basicity of heterogeneous catalysts such as alkali metal-modified zeolites [20][21][22][23] and smectites, [25], and SiO 2 -supported amines [29] show Table 4, one can see that the best-performing Zn-Mg-Al-O (Table 4, entry 1) has more basic sites (0.19 mmol/g) and lower H 0,max value (&8.9) than the other Zn-M-Al-O (M = Ca, Sr, and Ba) catalysts (Table 4, Table 4, entry 6) has much less total basic sites than the Zn-M-Al-O (M = Ca, Sr, and Ba) catalysts but shows sites with H 0 C 6.1 only slightly lower, consistent with the catalytic activity of the catalysts. In terms of basicity and catalytic activity, the better catalytic activity of Zn-M-Al-O is due to the appropriate basicity resulted from the modification of Zn-Al-O with the alkaline earth metals.…”

“…In the past decades, numerous catalysts have been studied for the cycloaddition reaction , e.g., metallic complexes [4][5][6][7], phosphines [8,9], organic bases [10][11][12], ionic liquids [13][14][15][16], metal oxides [17][18][19], modified molecular sieves [20][21][22][23][24] and smectite [25], and supported catalysts [26][27][28][29][30], etc. However, most of the high-efficiency ones are homogeneous catalysts, and the disadvantages are the high cost for catalysts fabrication (e.g., metallic complexes) and product separation.…”

Conversion of carbon dioxide to cyclic carbonates using diimine Ru(II) complexes as catalysts

“…The pressure was kept constant during the reaction. The vessel was then cooled to [5][6][7][8][9][10] • C in ice bath after the desired reaction time. The pressure was released, then the excess gases were vented.…”

“…The cyclic carbonates are widely used as organic synthetic intermediates, aprotic polar solvents, precursors for biomedical applications and as raw materials for engineering plastics. [5] Various catalysts have been developed for the synthesis of cyclic organic carbonates from CO 2 and epoxides, among which several homogeneous and heterogeneized salen complexes, [6] alkali metal halides, [7] organic bases, [8] metal oxides, [9] zeolite, [10] ionic liquids [11] and metal complexes [12] can be mentioned. While the advances have been significant, most of these catalysts currently suffer from low catalyst reactivity, the need for co-solvent or the requirement for high pressure and/or high temperature.…”

Synthesis of cyclic carbonates from carbon dioxide and epoxides using alkali metal halide supported liquid phase catalyst

“…The five membered cyclic carbonates have several application such as they act as a precursor for polycarbonates and other polymeric materials [3] they are also used as an intermediate for glycol, carbamates, pyrimidines, purines and so on [4]. In recent decades numerous homogenous and heterogeneous catalyst system such as alkali metal salts alone [5] or in combination with crown ether [6], quaternary ammonium salt or phosponium salt [7,8] ionic liquids [9], halostannanes [10] other organic bases [11][12][13], mixed oxides [14][15][16][17] smectite [18,19], zeolite [20,21] titanosilicates [22], metal complexes [23][24][25][26][27][28][29], and have been explored for this transformation. Most of these systems suffer from the problems associated with low catalyst reactivity, catalyst/product separation, expensive catalysts, sophisticated techniques and lower yield of the products.…”