The oxidative dehydrogenation of С1-С2 alcohols on copper-contained zeolites and HTSC
L.Akhalbedashvilia,
G. Maisuradzeb,
A. Mskhiladzec,
Sh. Sidamonidzeb
Summary
oxidative dehydrogenation of CH3OH and C2H5OH was studied on different matrix, containing copper, and compared with each other. It was found that Y123 and Bi2212 are less active to compare with Cu-containing zeolites. It should be mentioned that many uncertainties associated with the mechanism of the catalytic action of copper associates in high-temperature superconductors, as well as the localization, nature and mechanism of the catalytic action of Cu-ion sites in the copper-containing zeolites .: alcohols, zeolite, copper, oxidation
the oxidation reactions with molecular oxygen the oxides of transition metals (TM) are active catalysts due to the low activation energy of change the oxidation state that facilitates transfer the electrons between the substrate and catalyst. The specifity of zeolite catalysts in oxidation reactions is caused, on the one hand by the fact that the activity of the transition metals ™ cations fixed in the matrix depends on the coordination of skeleton with atoms, on the other hand, the matrix itself contributes to the formation and conversion of intermediate products as well as in the diffusion of reagents and reaction products. It should be noted that the catalytic transformation of alcohols on heterogeneous, including zeolite contacts studied quite extensively, but the conversion of methanol and ethanol in an oxidizing environment on zeolite catalysts today are still little studied.was previously shown [1-5] that the low activity of initial synthetic and natural zeolites in the oxidative conversion of methanol and ethanol due to the presence of molecular oxygen near the active alcohol adsorbed on the alkali cations, but the introduction of transition metals changes the nature of the catalytic action.this study it was carried out the comparison the activity of copper-containing catalysts on various zeolite and high-temperature superconductor (HTSC) carriers in the oxidative conversion of C1-C2 alcohols.
oxidative dehydrogenation alcohol zeolit ??
Experimental part
a matrix the synthetic zeolites Х, Y, mordenite, ZSM - 5 and natural zeolite clinoptilolite (CL) were applied; as the oxidic form high-temperature superconductors (HTSC) Y1Ba2Cu3Ox and Bi2Sr2CaCu3Ox were used. Zeolite catalysts were prepared by an ion-exchange method from solutions of copper-ammonia complexes and copper nitrate; HTSC-samples were synthesized by the traditional ceramic technique from the corresponding metal oxides. The catalytic experiments were carried out by the microflow method with varying of temperature, the size of catalyst grain and gas flow rate. The composition of the initial mixture and yields were analyzed chromatographically using porapac Q, porapac R and molecular sieve 13X as phases.
and discussion
of the ethanol in an oxidizing atmosphere at zeolite catalysts, as shown previously [2, 5] proceeds in four directions: the intermolecular and intramolecular dehydration to ether and ethylene, respectively, as well as complete to CO2 and partial oxidation to acetaldehyde (Scheme 1). Thus on initial NaX and NaY zeolites the intramolecular and intermolecular dehydration of ethanol pass through a maximum and in the range of lower temperature (550 - 650 K), in contrast to the oxidative reactions, ie, in deep and partial oxidation (Figure 1).
Scheme 1
Fig. 1.The relation of ethanol conversion products on NaY zeolite:
- (C2H5) 2O; 2 - C2H4; 3 - CH3CHO; 4 - CO2.
ethanol, methanol conversion on NaY proceeds a little differently - intermolecular dehydration, oxidative dehydrogenation to CH2O and full and partial oxidation to CO and CO2 (scheme 2).
Scheme 2
The temperature of reaction shifted to a higher temperature region (see Fig. 2). According to data the processes of oxidative dehydrogenation, dehydration and deep oxidation of alcohol on faujasite proceed simultaneously. Introduction the copper cations to the structure of Y zeolite sharply alters the nature of the conversion of alcohols (see Fig. 3).
Fig. 2.The relation of methanol conversion products on NaY zeolite:
1 - CH2O; 2 - (CH3) 2O; ...
