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The comprehensive understanding of the composition, behaviour and reactivity of a catalyst used inside industrial plants is an extremely hard task that is rarely achieved. It requires the use of different spectroscopic techniques, applied under in situor in operando conditions, and combined with the investigation of the catalyst activity. Often the operating experimental conditions are different from technique to technique and the different results must be compared with care. In the present contribution, we combined in situXANES/EXAFS, IR spectroscopy of adsorbed CO, CO chemisorption and catalytic tests performed using a pulse reactor in depletive mode. This multitechnical approach resulted in the understanding of the role that dopants (LiCl, KCl, CsCl, MgCl2LaCl3) have in the nature, relative fraction, reducibility and dispersion of Cu-phases on CuCl2/γ-Al2O3catalysts for oxychlorination reaction, a key step of the PVC chemistry. In the undoped catalyst two Cu phases coexist: Cu-aluminate and supported CuCl2, being the latter the only active one [J. Catal., 2000, 189, 91]. EXAFS and XANES highlighted that all dopants contribute more or less efficiently in increasing the fraction of the active copper species, that reaches a value of almost 100% in the case of MgCl2or LaCl3. EXAFS directly, and IR indirectly, proved that the addition of KCl or CsCl (and less efficiently of LiCl) results in the formation of mixed CuKxCl2+xor CuCsxCl2+xphases, so altering the chemical nature of the active phase. XANES spectroscopy indicates that addition of MgCl2or LaCl3does not affect the reducibility by ethylene (under static conditions) of the active CuCl2phase and that the reducibilility of the new copper-dopant mixed chloride are in the order CuCl2> CuLixCl2+x> CuKxCl2+x> CuCsxCl2+x. However, when reduction is done inside a pulse reactor, a more informative picture comes out. The last technique is able to differentiate all samples, and their ability to be reduced by ethylene resulted in the order: La- > Mg- > Li-doped > undoped > K- > Cs-doped catalyst. To understand this apparent discrepancy the dispersion of the active phase, measured by CO chemisorption, was needed: it has been found that addition of LiCl increases enormously the dispersion of the active phase, LaCl3significantly and MgCl2barely, while addition of both KCl and CsCl results in a decrease of the surface area of the active phase. The mechanism of the enhancing effect of La and Mg on catalytic activity is still not clear, but it could be associated to the modification that they induce to the support surface: the Cu is so highly dispersed that almost all is in direct contact with support surface. It is finally worth noticing that the previous EXAFS and XANES study allowed us to refer the chemisorption data to the active phase only, while the IR study allowed us to fix the Cu+/CO surface stoichiometry. Summarizing the use of a multidisciplinary approach has been the conditio sine qua non(mandatory condition) to understand the complex role that the different additives have on the active phase of the CuCl2/γ-Al2O3catalysts for ethylene oxychlorination. [ABSTRACT FROM AUTHOR]

Abstract: In two recent contributions [PCCP 12 (2010) 5605; Dalton Trans. 39 (2010) 8437], we combined in situ and in operando XANES/EXAFS, CO chemisorption and catalytic tests to elucidate the role that dopants (LiCl, KCl, CsCl, MgCl2 LaCl3) have in the nature, relative fraction, reducibility, and dispersion of Cu-phases on CuCl2/γ-Al2O3 catalysts for C2H4 oxychlorination reaction, a key step of PVC chemistry. In the present work, we extend these studies by investigating the effect that the dopants have on the nature, population, and strength of surface Lewis and Brønsted sites of the support, using IR spectroscopy of adsorbed CO at liquid nitrogen temperature. The doping eliminates all the surface Lewis acidity in CsCl- and KCl-doped catalysts and strongly suppresses it in the remaining cases. The increase of the strength of the Brønsted sites is remarkable in all cases but the CsCl-doped one. To understand both the effect of Cl- anions and dopant cations a set of dopant free, HCl-impregnated and of Cu-free dopant-impregnated supports have been investigated. Addition of chlorine decreases the density and the strength of Lewis sites, while it increases those of the Brønsted sites. Catalytic testing of each material revealed that formation of chlorinated by-products was directly correlated with the density of Lewis acid sites. Furthermore, an empirical correlation was found between the strength of the Brønsted acid sites of the support and the stretching frequency of CO adsorbed on the reduced fraction of the active copper chloride phase. The present study is aimed to complement the published literature on alumina, underlining the usefulness of the molecular approach made by IR spectroscopy low temperature adsorbed CO to investigate the surface of catalyst support. [Copyright &y& Elsevier]

A bifunctional catalyst comprising CuCl 2 /Al 2 O 3 and nitrogen-doped carbon was developed for an efficient one-pot ethylene oxychlorination process to produce vinyl chloride monomer (VCM) up to 76 % yield at 250 °C and under ambient pressure, which is higher than the conventional industrial two-step process (≈50 %) in a single pass. In the second bed, active sites containing N-functional groups on the metal-free N-doped carbon catalyzed both ethylene oxychlorination and ethylene dichloride (EDC) dehydrochlorination under the mild conditions. Benefitting from the bifunctionality of the N-doped carbon, VCM formation was intensified by the surface Cl*-looping of EDC dehydrochlorination and ethylene oxychlorination. Both reactions were enhanced by in situ consumption of surface Cl* by oxychlorination, in which Cl* was generated by EDC dehydrochlorination. This work offers a promising alternative pathway to VCM production via ethylene oxychlorination at mild conditions through a single pass reactor., (© 2020 The Authors. Published by Wiley-VCH GmbH.)