Abstract
Oxides (such as SiO2, TiO2, ZrO2, Al2O3, Fe2O3, CeO2) have often been used to prepare supported Pt catalysts for CO oxidation and other reactions, whereas metal phosphate-supported Pt catalysts for CO oxidation were rarely reported. Metal phosphates are a family of metal salts with high thermal stability and acid-base properties. Hydroxyapatite (Ca10(PO4)6(OH)2, denoted as Ca-P-O here) also has rich hydroxyls. Here we report a series of metal phosphate-supported Pt (Pt/M-P-O, M = Mg, Al, Ca, Fe, Co, Zn, La) catalysts for CO oxidation. Pt/Ca-P-O shows the highest activity. Relevant characterization was conducted using N2 adsorption-desorption, inductively coupled plasma (ICP) atomic emission spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), CO2 temperature-programmed desorption (CO2-TPD), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR). This work furnishes a new catalyst system for CO oxidation and other possible reactions.
Highlights
Heterogeneous metal catalysts are very useful in synthesizing chemicals, processing fuels, and ablating environmental pollutants [1]
It can be said that these conventional supported metal catalysts are at the heart of heterogeneous catalysis because they are so useful in a variety of reactions and the global market for these catalysts is huge
In a classic book written by Tanabe, Misono, Ono, and Hattori, metal phosphates are highlighted as a new family of solid acids showing some promising applications in heterogeneous catalysis [3]
Summary
Heterogeneous metal catalysts are very useful in synthesizing chemicals, processing fuels, and ablating environmental pollutants [1]. Typical oxide supports include SiO2, Al2O3, TiO2, ZrO2, Fe2O3, and CeO2 These supports, with good thermal stability and high surface areas (usually from 10 to 1000 m2/g) provide a platform for dispersing and stabilizing metal nanoparticles, and render the final catalysts various properties (e.g., acid-base, redox properties). Compared with metal oxides and carbons, metal salts have seldom been used in the preparation of supported metal catalysts [2] because many metal salts (e.g., most nitrates, chlorides, and sulfates) are soluble in water and are not thermally stable. These attributes make the preparation of heterogeneous catalysts a daunting task. Metal phosphates can be used as catalysts directly, for instance, in the partial oxidation of propane [4], oxidative dehydrogenation of isobutane to isobutene [5,6,7], oxidative dehydrogenation of ethylbenzene to styrene [8], dehydration of cyclohexanol and
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