ORIGINAL PAPER The Effects of PdZn Crystallite Size on Methanol Steam Reforming Robert A. Dagle Æ Ya-Huei Chin Æ Yong Wang Published online: 30 November 2007 Ó Springer Science+Business Media, LLC 2007 Abstract Exceptional activity and selectivity of Pd/ZnO catalysts for methanol steam reforming have been attrib- uted to the formation of PdZn alloy. In this paper, we evaluated the crystallite size effects of PdZn alloy on methanol steam reforming. An organic preparation method was used to avoid the complexity from the alteration of ZnO morphology typically associated with the conven- tional aqueous preparation method. Both Pd loading and reduction temperature ( [ 350 °C) were used to vary the crystallite size of PdZn alloy. Experimental activity studies and transmission electron microscope (TEM) character- izations indicated that formation of large sized PdZn crystallites exhibit high reactivity and low CO selectivity during methanol steam reforming. Keywords PdZn alloy  Pd/ZnO catalysts  PdZn crystallites  Methanol steam reforming  Hydrogen production 1 Introduction Among hydrocarbon fuels, methanol has been widely studied as a source of hydrogen production for the fuel cell due to its high hydrogen/carbon ratio, low sulfur content, and relatively low reforming temperature (250–350 °C). Due to the high energy density of methanol (*5.6 kWh/kg compared to *0.12 kWh/kg for lithium ion batteries), even a very inefficient chemical to electrical device could be a significant improvement over the available secondary battery technology [1]. The methanol steam reforming reaction, as shown in Eq. 1, produces three moles of hydrogen for every mole of methanol reacted. However, if significant amount of CO is formed, the water–gas-shift (WGS) reaction, shown in Eq. 2 is required to not only maximize hydrogen production but also minimize the CO poisoning of the fuel cell. CO produced by steam refor- mation must be reduced to ppm levels before introducing the reformate to the PEM fuel cell. CH 3 OHðgÞþ H 2 OðgÞ¼ 3H 2 ðgÞþ CO 2 ðgÞ; DH 0 ¼ 49:5 kg=mol ð1Þ COðgÞþ H 2 OðgÞ¼ CO 2 ðgÞþ H 2 ðgÞ; DH 0 ¼ 41 kg=mol ð2Þ Most research has focused on Cu-based catalysts which exhibit a high reactivity and selectivity to CO 2 and H 2 [2]. However, the Cu-based catalysts have significant disad- vantages, including their pyrophoric nature and the tendency to deactivate at high temperature ( [ *280 °C) [1, 2]. In addition, stability under certain oxidizing environ- ments is a concern [3]. On the other hand, group VIII metals exhibit different performance than copper based catalysts. Over Group VIII metal catalysts, methanol readily decomposes to CO and H 2 (Eq. 3), and require a separate WGS conversion unit. CH 3 OHðgÞ¼ COðgÞþ 2H 2 ðgÞ; DH 0 ¼ 90:7 kg=mol ð3Þ Iwasa et al. was the first to report that Pd supported on ZnO and reduced at [ 300 °C exhibits exceptional high selectivities to CO 2 and H 2 [4]. Combined TPR, XRD, XPS, and TEM methods revealed the formation of PdZn R. A. Dagle  Y.-H. Chin  Y. Wang (&) Pacific Northwest National Laboratory, 902 Battle Boulevard, P.O. Box 999, Richland, WA 99352, USA e-mail: yongwang@pnl.gov 123 Top Catal (2007) 46:358–362 DOI 10.1007/s11244-007-9009-4