XPS–SIMS Surface Characterization of Aluminovanadate Oxide Catalyst Precursors Co-Precipitated at Different pH: Effect of Calcination

Abstract

X-ray photoelectron spectroscopy and time-offlight secondary ion mass spectrometry were employed in a comparative study of the surface physical and chemical state of aluminovanadate oxide catalyst precursors (V-Al-O), which were precipitated in the range of pH from 5.5 to 10, after drying and calcination. Core-level photoelectron spectra, X-ray induced Auger and valence band spectra of the samples were measured so as to quantitatively evaluate the surface concentrations of the catalyst components. The binding energy shifts of the respective O 1s, V 2p and Al 2p lines were determined as a function of pH and analyzed in terms of the initial state effect related to the atomic charge and Madelung potential. The surface of the catalysts was composed of aluminum hydroxide/oxyhydroxide and of dispersed vanadium oxide species. Increasing pH was found to result in a monotonic variation of the elemental surface composition, modification of the valence band, progressive hydroxylation of the surface and increasing dispersion of vanadium oxide species. Increasing pH was also accompanied by an increase in the abundance of V 4? species, specific surface area and reducibility. Calcination in air at 500°C gave rise to surface segregation of vanadium, changes in the valence band and partial dehydroxylation. The structural transformations in vanadium oxide species and aluminium hydroxide support and their interaction were accompanied by an increasing abundance of V-O-Al bonds. The net result of the restructuring was a decrease in the specific surface area and reducibility of the calcined catalysts. The enhancement of the catalytic activity in propane oxidative dehydrogenation demonstrated by V-Al-O samples with increasing precipitation pH and after calcination was in good correlation with a growing population of the V 4? states and increasing nucleophilicity of oxygen sites.

Stability and luminescence properties of CsPbBr3/CdSe/Al core-shell quantum dots

“…The peak near 531.2 eV was traditionally attributed to the O 1s energy level in the Al-O bond of Al 2 O 3 , whereas the peak at 532.7 eV corresponds to the O 1s energy level in the Al-OH bond of Al(OH) 3 . [47][48][49] Interestingly, after five days, the peak at 531.2 eV progressively increased while the peak at 532.7 eV gradually faded, indicating that Al(OH) 3 would eventually dehydrate to become Al 2 O 3 in the natural environment, and the Al 2 O 3 layer had anti-oxidation and photodegradation properties. [26,46] As a result, the stability of the CsPbBr 3 QDs was significantly improved following the addition of Al.…”

Thermal Decomposition of Nickel Oxalate Dihydrate: A Detailed XPS Insight

“…The modified Auger parameter (AP) α′, defined as a sum of the BE of particular photoelectrons ejected from an element and the kinetic energy (KE) of X-ray excited Auger electrons emitted from this element, is unsusceptible to charging effects. Instead, the AP is sensitive to the local chemical and structural states of atoms and therefore particularly useful in characterizing materials. − In the as-prepared state of Ni oxalate, the APs for nickel and oxygen are, respectively, α′(Ni) = BE­(Ni 2p 3/2 ) + KE­(Ni L 3 M 45 M 45 ) = 1697.8 eV and α′(O) = BE­(O 1s) + KE­(O KL 23 L 23 ) = 1040.9 eV. With the temperature rising up to 250 °C, α′(Ni) gradually increases by ∼0.9 eV, with a step occurring at 150–205 °C.…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…With the majority of reactions occurring at the catalyst surface, techniques that examine the physical and chemical properties of the catalyst surface and its interactions with reactants and poisons are becoming increasingly popular. Chenakin et al 321 discussed the surface characterisation of aluminovanadate oxide catalyst precursors using a combination of XPS and TOF-SIMS. Samples were prepared by coprecipitation of Al(NO 3 ) 3 $9H 2 O and NH 4 VO 3 from aqueous solution at varying pH followed by drying and calcining.…”