Methane Combustion Over Copper Chromites Catalysts Prepared by the Sol–Gel Process

Abstract

Methane combustion was performed over a series of copper chromites (CuCr 2 O 4 ) catalysts prepared by the sol-gel process (SG). The results were compared with those obtained over commercial CuCr 2 O 4 . The samples were characterised by elemental analysis, thermal analysis, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The as-synthesised CuCr 2 O 4 sample exhibited higher specific surface area (248 m 2 g -1 ) with respect to commercial solids (42 m 2 g -1 ). The surface properties were established using XPS. Simultaneously, an increase in the atomic Cr 6? /Cr 3? ratio (0.56 for SG catalyst vs. 0.39 for commercial sample) and a decreasing surface copper concentration (8.3%, for SG specimen vs. 17.6% for commercial catalyst) are observed. XPS study revealed also that Cu 2? /(Cu°? Cu ? ) ratio of copper species remained constant (ca. 5) in both catalysts. Structure transformations of CuCr 2 O 4 under reduction-reoxidation conditions showed that the reduction of copper and/or chromium cations from the CuCr 2 O 4 and from delafossite (CuCrO 2 ) structure (CuCr 2 O 4 $CuCrO 2 ? Cu ? Cr 2 O 3 $Cu ? Cr 2 O 3 ) were different. This has lead to a difference in catalytic properties of the catalysts. Catalytic activity of SG catalysts was superior to that of commercial CuCr 2 O 4 tested under the same conditions. Complex hysteresis behaviour for CuCr 2 O 4 catalysts ramped over a temperature range of 220-850°C where the stables active phases were obtained only after the first ramp of heating under reactants. No catalysts deactivation was further observed after several cycles of heating and cooling. The stabilisation of catalytic activity was attributed to the formation of mixed crystalline phases containing both copper and chromium species.

Enhancing the performance of SBA-15-supported copper catalysts by chromium addition for the chemoselective hydrogenation of trans-cinnamaldehyde

“…According to the literature, these energy values depend on the sample composition, crystallinity, and particularly on the copper micro-environment. 1,[64][65][66][67] For instance, the BE for bulk CuO is 932.4 eV. 68 Accordingly, the decrease in the binding energy from 934.25 eV to 933.6 eV can arise from the decrease in CuO dispersion with the increase in copper content, which is in good agreement with the XRD results.…”

Effect of the Nuclearity and Coordination of Cu and Fe Sites in β Zeolites on the Oxidation of Hydrocarbons

“…Table compares the activities of the most active Al-rich Cu-*BEA with supported and oxidelike Cu catalysts, Ce-, Co-, Fe-, and Mn-based catalysts of various structures and compositions, and supported Pd catalysts found in the literature. The T 50 value for the Al-rich Cu-*BEA is 407 °C, while for the supported and mixed Cu-oxo catalyst, it is typically in the 450–550 °C − range. The supported and mixed Cu-oxo catalysts generally exhibit lower activity than the Al-rich Cu-*BEA.…”

Cu/Mn-based mixed oxides derived from hydrotalcite-like precursors as catalysts for methane combustion

“…4,. A number of works address the role of the catalyst preparation method and the nature of the oxide precursor [15,19,20,30,31,33,[40][41][42][43]. In particular, the use of precursors related to the naturally occurring mineral known under the name of hydrotalcite has been indicated as providing particularly active mixed oxide catalysts [24,27,34,35,39,45,46].…”