Near-infrared spectroscopy of palladium-containing layered double hydroxides used as catalysts

Three catalysts consisting of layered double hydroxides (LDHs) of magnesium and aluminum, and containing palladium in various forms, were synthesized and subsequently characterized by mid- and near-infrared spectroscopies. The results thus obtained are compared with those for a pure Mg/Al layered double hydroxide. The spectra for the Pd-containing LDHs (particularly the strength of the bands) were found to depend on the particular palladium form present. As a rule, the mid-infrared spectra contained a strong, broad band at 3800–2500 cm−1 due to stretching vibrations of the different types of hydroxyl groups present in the solids and another signal at ca. 1370 cm−1 due to the presence of carbonate ions in the interlayer region. These signals were the strongest in the near-infrared spectra, which were also quite similar, roughly, for all solids.

Research highlights
► We use for the first time the NIR spectroscopy to characterize palladium supported over hydrotalcites catalysts.
► The catalysts exhibited three distinct zones with marked differences in fundamental stretching vibrations of OH groups.
► The NIR region allowed the pure LDH to be discriminated from the Pd-containing catalysts on the basis of the presence of electronic bands due to the metal.