Characterisation of ceria supported chromia catalysts
TL;DR: A series of ceria supported chromia catalysts of different loading were prepared and the effect of support in stabilising various chemical and molecular states of chromium with the calcination temperature were studied as discussed by the authors.
Abstract: A series of ceria supported chromia catalysts of different loading were prepared and the effect of support in stabilising various chemical and molecular states of chromium with the calcination temperature were studied. XRD results showed that the chromia phase is randomly dispersed, disordered, and the crystallite size may be smaller than the detection limit. BET surface area and pore volume results suggested some plugging of pores on the support by chromia phase. EGA analysis suggested the existence of the surface heterogenity involving weakly and strongly chemisorbed CO 2 . EGA and NIR DRS studies revealed the bulk-like behaviour in the catalysts having chromia loading of more than 5 wt.%. EGA, FTIR and UV–VIS–DRS studies supported the formation of anchored surface chromium species. Moreover, the nature of molecular states of chromium and the coordinative environment under various thermal conditions were investigated using FTIR and UV–VIS–DRS techniques.
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TL;DR: In this paper, a review of the most popular IR spectroscopy applications for catalytic applications is presented, starting from the very general basis of the spectroscopic method applied and focusing on the adsorption of chelating compounds on surfaces of mineral oxides.
433 citations
TL;DR: Various chromium-containing catalysts were tested for the total oxidation of trichloroethylene (TCE) as a model reaction for the catalytic combustion of chlorinated organic pollutants to demonstrate higher activity and higher CO2 selectivity than traditional alumina supported chromia.
Abstract: Various chromium-containing catalysts were tested for the total oxidation of trichloroethylene (TCE) as a model reaction for the catalytic combustion of chlorinated organic pollutants. A spinel-type cobalt chromite (CoCr2O4) among others was proven to be a very promising catalyst showing higher activity and higher CO2 selectivity than traditional alumina supported chromia. Even if both Cr3+ and Cr6+ species were observed on the surface of CoCr2O4, the Cr6+ species was stable under reducing environment. The presence of Cr3+-Cr6+ pair sites and the effect of redox treatments on the activity were investigated to explain the nature of possible active sites for TCE decomposition. Higher selectivity to CO2 of CoCr2O4 was ascribed to the abundance of its Cr3+ species, together with its activity for water gas shift reaction.
108 citations
TL;DR: In this paper, a possible pathway of soot oxidation over Cu0.05Ce0.95-CA is proposed, based on the relationship of the performance and physicochemical features of catalysts, which pathway follows the mechanism associated with redox couple and oxygen spill over effect.
62 citations
TL;DR: In this paper, the role of chromium oxides and ceria and their synergistic effect in textural properties, redox performance and surface species over the Cr1−xCex/TP catalysts were investigated in detail by means of Brunauer-Emmertt-Teller (BET) surface area analysis, X-ray diffraction (XRD), transmission electron microscope (TEM), temperature-programmed reduction of H2 (H2-TPR), NO-TPD), photoluminescence spectra, and in situ diffuse reflectance infrared
32 citations
TL;DR: In this paper, mesoporous ceria and SBA-15 silica were modified with iron and chromium oxide nanoparticles and characterized by XRD, N2-physisorption, FTIR, UV-vis, Moessbauer spectroscopy and TPR-TG in hydrogen.
30 citations
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TL;DR: In this paper, the authors measured the reflectance spectra of ten crystalline chromate salts and compared them with the spectrum of the chromate ion in solution, and found that the increase in the intensity of the 23,000 cm − 1 band in crystalline compounds can be explained by the increasing polarizing effect of the cations and the appearance of new low-energy bands in case of highly covalent metal.
32 citations
TL;DR: In this article, the mobility of inorganic oxides has been investigated by combined diffuse reflectance (DR) and spectroscopies as a function of the Cr oxidation state, the type of======inorganic oxide (silica, alumina and mordenite) and the environmental conditions (hydrated and dehydrated state).
Abstract: The mobility of Cr
n+
in inorganic oxides has
been investigated by combined diffuse reflectance (DR)–EPR
spectroscopies as a function of the Cr oxidation state, the type of
inorganic oxide (silica, alumina and mordenite) and the environmental
conditions (hydrated and dehydrated state). Cr
n+
ions are mobile under hydrated and dehydrated conditions and
Cr
n+
preferentially migrates from silica to
alumina and, to a lesser extent, to mordenite, although only a small
amount of migration of Cr
n+
is observed from
alumina to mordenite and vice versa. The observed
preference sequences are discussed in relation to the properties of
the inorganic oxides.
25 citations
TL;DR: In this paper, a temperature-programmed calcination of basic chromium(III) acetate impregnated onto a high surface area silica support was studied by quadrupole mass spectrometry and infrared spectroscopy.
Abstract: Temperature-programmed calcination of basic chromium(III) acetate impregnated onto a high surface area silica support and chromium(III) acetylacetonate dry-blended with silica has been studied by quadrupole mass spectrometry and infrared spectroscopy. In both cases the same reactive intermediate has been identified.
25 citations
TL;DR: Instrumental neutron activation analysis (INAA), atomic absorption spectrometry (AAS) and ultraviolet/visible (UV/VIS) spectrophotometry were applied as independent methods to the determination of chromium in Phillips-type polymerization catalysts as mentioned in this paper.
Abstract: Instrumental neutron-activation analysis (INAA), atomic absorption spectrometry (AAS) and ultraviolet/visible (UV/VIS) spectrophotometry were applied as independent methods to the determination of chromium in Phillips-type polymerization catalysts. Catalysts were prepared in the gas phase, using chromium oxychloride vapour as the adsorbate and silica as the support. From freshly prepared catalysts, chromium was quantitatively brought into solution with de-ionized water, enabling its rapid determination as chromate by UV/VIS spectrophotometry. The use of INAA and AAS in addition to UV/VIS spectrophotometry allowed the quantitative nature of the release of chromium from silica with de-ionized water to be verified, the accuracy of the chromium determination to be checked and the speciation of chromium between the oxidation states +3 and +6 to be determined.
16 citations
Journal Article•
TL;DR: In this paper, the processes proceeding in catalysts at the interface of the metal oxide and the support are considered, and experimental results related to the oxide-oxide interaction are summarized for Ni, Co and Fe oxides supported on various oxide carriers.
Abstract: The processes proceeding in catalysts at the interface of the metal oxide and the support are considered. For Ni, Co, and Fe oxides supported on various oxide carriers, experimental results related to the oxide-oxide interaction are summarized. Attention is focused mainly on systems prepared by the impregnation method. Oxide-oxide interactions are systematized on the basis of the chemical nature of the supported metal
11 citations