3 - CO2; 4 - unreacted CH3ОН
Fig. 3.The relation of methanol conversion products on CuNaY:
1 - CH2O; 2 - (CH3) 2O; 3 - CO2; 4 - unreacted CH3ОН
The catalytic activity of initial mordenite and especially of ZSM - 5 is extremely low up to 773 K and introduction of Cu2 + in their structure and formation of coordinative-unsaturated isolated Cu (II) ions with symmetry of plane square result in appearance of high activity and selectivity in deep oxidation of alcohols.initial CL ethanol and methanol and formed C2H4, CH3CHO and CH2O undergo to full oxidation at temperature high than 623K (fig.4). The reactions as complete and partial oxidation, so intermolecular dehydration of methanol and ethanol up to dimethyl ether and С2Н4 accordingly begins on CuCL from 493 K.The ethoxy ethane in yields of a reaction missed. The dehydration of ethanol to C2H4 prevails up to 553 К, and the degree of conversion up to СН3СНО does not exceed 10% in all temperature range (fig.5).
Fig.4. Dependence of ethanol conversion products on temperature on initial CL: 1 - unreacted C2H5OH; 2 - C2H4; 3 - CH3CHO; 4 - CO2
.4. Dependence of ethanol conversion products on temperature on CuCL: 1 - unreacted C2H5OH; 2 - C2H4; 3 - CH3CHO; 4 - CO2
conversion of ethanol on zeolites occur under two parallel - consecutive paths:
Scheme 3
Scheme 4
4 prevails.of methanol conversion to СН2О occurs by formation of methylene groups with following oxidation according scheme 5:
5
major reaction products on HTSC in conversion of alcohols were aldehydes, CO2, CO (fig.6, 7). Neither ethers nor C2H4 and H2 were detected. The catalytic activity of Bi2Sr2CaCu3Ox in oxidative dehydrogenation and deep oxidation was much lower than of Y1Ba2Cu3Ox [6]. It may be suggested that the observed difference in activity and in the mechanism of alcohol conversion can be caused by the structural differences between Y1Ba2Cu3Ox and Bi2Sr2CaCu3Ox - the difference in the number of CuO-CuO2 layers per unit cell, or in the number of active centers ; as well as different coordination environments of these centers, and their different accessibilities to reagent molecules.
Fig.6. The relation of methanol conversion products on Y1Ba2Cu3Ox: 1 - СН2О; 2 - СО; 3 - СО2; 4 - unreacred СН3ВІН
Fig.7. The relation of methanol conversion products on Bi2Sr2CaCu3Ox: 1 - СН2О; 2 - СО; 3 - СО2; 4 - unreacted СН3ВІН
of many studies of catalytic properties of copper-based systems - oxides Cu (II) and Cu (I), various kinds of mixed cuprates, copper-contained zeolites - in heterogeneous catalytic reactions lead to the conclusion that the high catalytic activity of these compounds is associated with the active centers formed by copper atoms in a particular charge state and coordination environment [1, 7, 8, 9], and in high-temperature superconductors is due to the presence of non-stoichiometric labile oxygen.the obtained data follows that copper-exchanged Y zeolites are characterized with the greatest total activity. They differ by the lowest temperatures of conversion of alcohols and high oxidative ability. On an example of CuNaY samples is clearly that not only nature and amount of a substituting cation, but also its state in a zeolite matrix, which, in turn, depends on conditions of heat treatment and ion exchange, substantially define a direction and depth of catalytic process.is known that on zeolites, not containing transition metals, the conversion of methanol is carried out according the acid-base mechanism with the formation of DME [10]. Moreover, it is now established that the interaction of zeolite with the OH- of methanol promotes to release CH3 + ions, which are intermediates in reactions catalyzed by protons and can exist freely in zeolites [11]. On the other hand, the monovalent cations are not active centers of the redox processes [12] .influence of conditions of modifying on a state of a cation is proved both with our catalytic data. It is known that at рН=5 the formation of cluster structures as a result of hydrolysis of using salt is carried out with participation of OH-groups. The heat treatment causes formation of clusters of copper ions, which exchange interaction causes weakening of EPR-signal strength [10]. The identical clusters, which include non-lattice oxygen, determine high catalytic activity in deep oxidation of alcohols. The mobility and reactivity of copper clusters is incremented also by additional coordination of copper ions with reagent molecules. The sample prepared at рН=10 contains the copper ions, which are coordinated with ammonia molecules at the expense of the greater coordination ability of NH3 in comparison with OH- groups. Such com...
