Metal Phosphides: Preparation, Characterization and Catalytic Reactivity
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REVIEW ARTICLE
Metal Phosphides: Preparation, Characterization and Catalytic Reactivity Roel Prins • Mark E. Bussell
Received: 15 August 2012 / Accepted: 15 October 2012 / Published online: 9 November 2012 Ó Springer Science+Business Media New York 2012
Abstract The preparation, characterization, and catalytic activity of supported metal phosphides are reviewed. Reduction of metal compounds together with phosphate is a convenient method to prepare metal phosphides, but requires high temperature. Reduction with phosphite, hypophosphite, or phosphine and the plasma reduction of phosphate can be carried out at lower temperatures, which leads to smaller metal phosphide particles and more active catalysts. Organometallic routes allow the separate synthesis of metal phosphide nanoparticles, which have to be added to the support in a second step. LEED, STM, XPS, and DFT studies have shown that the surfaces of Ni2P reconstruct to P-rich surfaces. The investigation of metal phosphides as catalysts for hydrotreating reactions continues to be a topic of considerable research with recent advances realized in using bimetallic and noble metal phosphides to achieve high activities and tailored selectivities. Finally, hydrodeoxygenation catalysis over metal phosphides is a growing area of research given the need to develop catalysts for upgrading biomass to transportation fuels. Keywords High temperature reduction Phosphate Low temperature reduction Phosphite Hypophosphite
R. Prins Institute for Chemical and Bioengineering, ETH Zurich, 8093 Zurich, Switzerland e-mail: [email protected] M. E. Bussell (&) Department of Chemistry, MS-9150, Western Washington University, Bellingham, WA 98225, USA e-mail: [email protected]
Phosphine Trialkylphosphine LEED Ni2P STM Ni2P Bimetallic phosphides Noble metal phosphides HDS, HDN, HDO
1 Introduction Transition metal phosphides are an interesting class of materials and worth investigating on the nanoscale because of their wide scope of properties and applications. Used as catalytic materials, metal-rich phosphides show excellent activity for hydrogenation reactions. For instance, nickel and rhodium phosphides catalyze the hydrogenation of acetylene to ethylene [1], Ni2P the hydrogenation of butadiene to butane [2], while iron, cobalt, nickel, molybdenum, and tungsten phosphides are active catalysts in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions [3–6]. HDS is the removal of sulfur atoms and HDN is the removal of nitrogen atoms from sulfur- and nitrogen-containing molecules, respectively, in petroleum feedstocks. Legislation that has been introduced over past years in many parts of the world demands very low sulfur levels in fuels. Because of this urgent need for lowering the sulfur level, improvements of the industrial HDS process have been ongoing for many years [7, 8]. As a consequence, research into the improvement of hydrotreating catalysts that remove sulfur and nitrogen atoms from oil fractions by HDS and HDN has been intensified. Metal
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