Application of microemulsion method for development of methanol steam reforming Pd/ZnO catalysts

Journal of Thermal Analysis and Calorimetry, May 2016

Thermal decomposition of palladium acetylacetonate adsorbed on zinc oxide (ZnO), and the formation of palladium oxide (PdO) and palladium zinc alloy (PdZn) phases were studied. Two types of ZnO supports were prepared by the microemulsion method using different surfactants, i.e. hexadecyltrimethylammonium bromide (CTAB) and (Bis(2-ethylhexyl) sulfosuccinate sodium salt, AOT). The nanoparticles of ZnO synthesized in the presence of CTAB surfactant showed higher specific surface area, smaller crystallite size and more irregular shape. Palladium was loaded on the surface of obtained supports by the impregnation method from the acetone solution of palladium acetylacetonate. Thermogravimetric studies indicated that palladium precursor loaded on CTAB-modified ZnO support was less stable and simultaneously decomposed in broader range of temperatures. Slight differences between the forms of precursors adsorbed on the supports were demonstrated by the diffuse reflectance infrared Fourier transform spectroscopy studies. Thermal decomposition of palladium acetylacetonate precursors in the air led to the formation of PdO species. The influence of ZnO morphology on the metal–oxygen bonds strength in PdO and formation of active phases were observed. Strongly dispersed PdZn crystallites on ZnO supports were formed upon reduction at 350 °C. Smaller crystallites of the size equal to 6.5 nm were detected in the Pd/ZnO-AOT catalysts.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2Fs10973-016-5525-4.pdf

Application of microemulsion method for development of methanol steam reforming Pd/ZnO catalysts

J Therm Anal Calorim Application of microemulsion method for development of methanol steam reforming Pd/ZnO catalysts Justyna Pawlonka 0 1 Wojciech Gac 0 1 Magdalena Greluk 0 1 Grzegorz Słowik 0 1 0 Department of Chemical Technology, Faculty of Chemistry, Maria Curie-Sklodowska University , 3 M. Curie-Sklodowska Sq., 20-031 Lublin , Poland 1 & Wojciech Gac Thermal decomposition of palladium acetylacetonate adsorbed on zinc oxide (ZnO), and the formation of palladium oxide (PdO) and palladium zinc alloy (PdZn) phases were studied. Two types of ZnO supports were prepared by the microemulsion method using different surfactants, i.e. hexadecyltrimethylammonium bromide (CTAB) and (Bis(2-ethylhexyl) sulfosuccinate sodium salt, AOT). The nanoparticles of ZnO synthesized in the presence of CTAB surfactant showed higher specific surface area, smaller crystallite size and more irregular shape. Palladium was loaded on the surface of obtained supports by the impregnation method from the acetone solution of palladium acetylacetonate. Thermogravimetric studies indicated that palladium precursor loaded on CTAB-modified ZnO support was less stable and simultaneously decomposed in broader range of temperatures. Slight differences between the forms of precursors adsorbed on the supports were demonstrated by the diffuse reflectance infrared Fourier transform spectroscopy studies. Thermal decomposition of palladium acetylacetonate precursors in the air led to the formation of PdO species. The influence of ZnO morphology on the metal-oxygen bonds strength in PdO and formation of active phases were observed. Strongly dispersed PdZn crystallites on ZnO supports were formed upon reduction at 350 C. Smaller crystallites of the size equal to 6.5 nm were detected in the Pd/ZnO-AOT catalysts. Palladium acetylacetonate; Zinc oxide; TG; DRIFTS; TPR; Decomposition Introduction Supported palladium catalysts have been widely used for oxidation and hydrogenation reactions of numerous chemical compounds [ 1, 2 ]. In recent years, a lot of attention has been paid to the development of supported palladium alloy catalysts, such as PdZn, PdIn or PdGa, showing their superior activity and selectivity in the hydrogenation of carbon oxides to methanol, water gas shift reaction, methanol steam reforming or hydrogenation of alkenes and alkadienes [ 3–7 ]. The impregnation method from aqueous solutions is one of simplest ways of the preparation of catalysts and has been often used for the synthesis of alumina-, silica- or carbon-supported palladium catalysts. It is well-accepted opinion that the support plays the crucial role in the formation of small crystallites and thus influences the activity, selectivity and durability of catalysts [8]. The formation of active sites in Pd/ZnO catalysts is a complex process and includes (1) adsorption of metal precursor on the support surface, (2) thermal decomposition of the metal precursor to oxide form (or directly to metallic form) and (3) reduction of oxide species to metallic palladium. The surface or bulk PdZn alloy phases are formed at elevated temperatures as a result of enhanced reduction of ZnO in the presence of metallic palladium. It has been often claimed that the size of PdO and Pd particles, PdO stability, interactions with the support and also catalytic performance of catalysts can be influenced by nature of palladium precursors [ 9–11 ]. Palladium nitrate Pd(NO3)2, tetraamminepalladium(II) nitrate Pd(NH3)4(NO3)2, tetraamminepalladium(II) chloride Pd(NH3)4Cl2 as well as palladium chloride PdCl2 belong to the most popular precursors used for preparation of catalysts, and their application in the impregnation method has been mostly determined by the isoelectric point (IEP) of the supports. Several papers demonstrated beneficial properties of palladium catalysts obtained by impregnation of the supports from nonaqueous solutions of organometallic complexes, such as palladium acetylacetonate (Pd(acac)2) [ 12, 13 ]. The use of aqueous solution may lead to the uncontrolled growth of palladium oxide species during drying and precursor decomposition. The way of adsorption of Pd(acac)2 on the oxide supports and transformation of the complex to palladium crystallites are still under debate. Palladium in the planar Pd(acac)2 complex is coordinated with two bidentate acetylacetonate ligands. bdiketonate ligands may interact with hydroxyl groups or defect sites on the supports, leading to the formation of hydrogen bonds or disruption of Pd-acetylacetonate ligand bonds with ligand exchange [ 14, 15 ]. There are a few works related to bulk and supported Pd(acac)2 decomposition [ 16–18 ]. Such phenomena have not been well documented for Pd/ZnO systems. The properties of metal oxide supports can be modified by the changes of precipitation conditions, thermal treatment or introduction of secondary elements. The promising preparation method of ZnO with suitable structural and surface properties is p (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2Fs10973-016-5525-4.pdf

Justyna Pawlonka, Wojciech Gac, Magdalena Greluk, Grzegorz Słowik. Application of microemulsion method for development of methanol steam reforming Pd/ZnO catalysts, Journal of Thermal Analysis and Calorimetry, 2016, pp. 1265-1272, Volume 125, Issue 3, DOI: 10.1007/s10973-016-5525-4