Abstract
Alumina supported CuCl2, the basic catalyst for ethylene oxychlorination, has been investigated by UV-Vis spectroscopy, EPR, EXAFS and XANES in a wide range (0.25-9.0 wt%) of Cu concentration. We have evidenced that, at low Cu content, the formation of a surface aluminate species takes place. The formation of this surface copper aluminate stops at 0.95 wt% Cu / 100 m2; at higher Cu concentrations excess copper chloride precipitates directly from solution during the drying step forming an highly dispersed CuCl2.H2O, phase, overlapping progressively the surface aluminate. Depletion tests and IR spectroscopy of adsorbed NO have demonstrated that the latter is the only active phase. A complete catalytic cycle has then been performed on CuCl2/Al2O3 catalyst. EPR, XANES and EXAFS, have been used to demonstrate that the ethylene oxychlorination reaction: C2H4 + 2HCl + ½ O2 --> C2H4Cl2 + H2O follows a three steps mechanism: (i) reduction of CuCl2 to CuCl (2CuCl2 + C2H4 --> C2H4Cl2 + 2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl + ½ O2 --> Cu2OCl2) and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2 + 2HCl --> 2CuCl2 + H2O). Finally, we have shown that time resolved, in situ, spectroscopy is a very promising technique to investigate the interplay between catalyst activity and oxidation state of copper.
Highlights
Production of VCM is based on cracking of 1,2-dichloroethane (EDC), which in its turn is produced by two parallel processes, oxychlorination: C2H4 + 2HCl + 1⁄2 O2 → C2H4Cl2 + H2O
It has been hypothesized that the first family, prevailing at low Cu concentration, could result from the interaction between CuCl2 and the Al2O3 carrier, while the second family, prevailing at high Cu concentration, could be the product of the surface precipitation of Cu compounds from the impregnating solution
In a successive work [27], we have studied the interaction of the base catalyst with ethylene showing that only CuCl2 is reactive to this reagent
Summary
Due to its relevant industrial impact, several papers have been devoted to its study [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] From these studies, the existence, on base catalyst, of two different Cu compounds is clearly emerging. The identification of the nature and the range of existence of Cu species has been achieved only very recently [24,25,26] This goal was accomplished only after a complete study on the effects that aging and thermal treatments have on the catalysts as a function of Cu loading. After a brief summary of the previous works, the separate interaction with oxygen and hydrochloric acid will be investigated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
