Pt−Ba/Al₂O₃ NSR Catalysts at Different Ba Loading: Characterization of Morphological, Structural, and Surface Properties

Abstract

Morphological, textural, and surface properties of several Pt-Ba/Al 2 O 3 NO x storage reduction (NSR) catalysts at different Ba loading in the range 0-30 wt % were characterized by means of X-ray diffraction, highresolution transmission electron microscopy, and Fourier-tranform infrared (FT-IR) spectroscopy using CO, CO 2 , and CH 3 CN as probe molecules. Upon increasing the Ba loading, the Pt exposure progressively decreased, accounting for sintering and masking of the Pt particles by Ba, whereas the interaction between Pt and the barium oxide phase increased. After a few cycles of heating in NO 2 and subsequent evacuation (conditioning treatment), BaCO 3 initially present evolved to Ba(NO 3 ) 2 and then decomposed into a well-dispersed nanosized BaO phase. Upon conditioning, a slight sintering of Pt is observed. However, the presence of Ba avoided a more stressed sintering, as it occurred for the Pt/Al 2 O 3 sample. Investigation by CO 2 and CH 3 CN adsorption followed by FT-IR spectroscopy revealed a high heterogeneity at the BaO surface. In particular, upon CO 2 adsorption a variety of surface carbonate-like species were formed (mainly bridging and chelating carbonates on Ba sites). The most relevant features upon CH 3 CN adsorption were the formation of anionic species on strongly basic oxygen ions of Ba 2+ O 2pairs and the presence of acetonitrile molecules polarized by highly uncoordinated Ba 2+ ions, stable under evacuation at room temperature. The FT-IR characterization with the three test molecules suggests that the best spread of the Ba phase is obtained for a loading between 16 and 23 wt %.

Selective Oxidation of Methanol to Hydrogen over Gold Catalysts Promoted by Alkaline‐Earth‐Metal and Lanthanum Oxides

“…With all g-Al 2 O 3 -supported catalysts, the promoter oxide was highly dispersed over the support, as was indicated by the absence of any X-ray diffraction (XRD) lines besides those related to g-Al 2 O 3 . [18] Only in the case of AuSrO/ Al 2 O 3 could a crystalline SrCO 3 phase be observed. The Au particle size distribution was determined by (scanning) transmission electron microscopy (STEM; Figure 1; see also Supporting Information).…”

Alkaline- and alkaline-earth oxides based Lean NOx Traps: Effect of the storage component on the catalytic reactivity

“…[17]. Experiments recently performed on freshly PtK/Al 2 O 3 catalyst [18] showed the characteristic peaks of ␥-Al 2 O 3 ; monoclinic K 2 CO 3 (JCPDS 16-820) and cubic K 2 O (JCPDS 23-493) phases were also hardly recognized.…”

Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

“…Consequently, the surface species comprised a mixture of newly formed carbonates and unreleased nitrates. As the DRIFT spectra of carbonates partially overlapped with nitrates, the gradually growing bands around 1592 cm −1 and 1320 cm −1 were tentatively ascribed to newly formed carbonates [41]. The location of these carbonate species deviated somewhat from those replaced by NO x during the storage process (negative peaks at 1535 and 1322 cm −1 ).…”