Enthalpies of reduction–oxidation of alumina-supported platinum

✍ Scribed by Chen-Bin Wang; Hung-Kuan Lin; Sung-Nien Hsu; Tzung-Huei Huang; Hui-Chi Chiu

• Book ID: 104422053
• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 108 KB
• Volume: 188
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(02)00332-1

✦ Synopsis

A calorimetric technique is described for measuring the reaction enthalpies of reduction of PtO x /Al 2 O 3 with hydrogen and oxidation of Pt/Al 2 O 3 with oxygen. The enthalpies of reduction-oxidation were determined at T red = 670 and T ox = 770 K for PtO x /Al 2 O 3 and Pt/Al 2 O 3 , respectively. The measurements revealed that the heat of reduction ( H red ) is relatively constant and has a value of -103 kJ ± 3 kJ (mol H 2 ) -1 for various platinum oxides. The particle size of platinum metals, however, had a profound effect on the bulk oxide formed and heat of oxide formation ( H f ). The platinum oxide formed at 770 K was PtO 2 for d < 2.0 nm, but this became Pt 2 O for d > 4.0 nm. The H f also varied with platinum oxide species from -190 kJ (mol O 2 ) -1 for PtO 2 to -168 kJ (mol O 2 ) -1 for Pt 2 O. Based on a thermodynamic cycle, it was demonstrated that the consistency in H red for various platinum oxides was attributed to the variations of heat of adsorption of water ( H ad,H 2 O ) on alumina-supported platinum.