A103 Surface Science 115 (1982) 61-78 Noi:th-Holland Publishing Company MODIFICATIONS OF THE SURFACE REACTIVITY OF Ni(100) BY STRUCTURED OVERLAYERS OF SULFUR: SELECTIVITY CHANGES FOR ETHANOL AND ISOPROPANOL DECOMPOSITION S.W. JOHNSON * and R.J. MADIX Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA Received 7 July 1981; accepted for publication 28 October 1981 61 The reactions of ethanol and isopropanol were studied on Ni(100), Ni(100) p(2X2)S and Ni(100) c(2 X 2)S by temperature programmed reaction spectroscopy (TPRS). On both Ni(100) and Ni(100) p(2X2)S decomposition to adsorbed CO and atomic hydrogen dominated the reaction. Methane was also formed by the reaction of adsorbed hydrogen atoms with fragments of the decomposition, most likely carbon atoms. On ~ooth surfaces evidence for a COH complex was observed, similar to previous results with methanol. On Ni(100) c(2X2)S the selectivity of the reactions changed dramatically. Formation of aldehydes was enhanced at the expense of CO and H2; methane was not observed. From these results it appears that alkoxy intermediates formed on all three surfaces by dehydrogenation and that their further decomposition to CO, Hta ) and Cta) was limited by adsorbed sulfur. Surface Science 115 (1982) 79-90 North-Holland Publishing Company NEW SURFACE STRUCTURE ANALYSIS OF Ag-Si PHASE BY QUANTITATIVE AUGER ELECTRON SPECTROSCOPY METHOD H. TOKUTAKA, K. NISHIMORI, S. NOMURA, A. TANAKA and K. TAKASHIMA Department of Electronics, Faculty of Engineering, Tottori University, Koyama, Tottori, Japan Received 14 July 1981; accepted for publication 19 October 1981 79 Ag or Au was deposited on a clean Si substrate at room temperature. These systems, Ag/Si and Au/Si, were annealed at various temperatures or various heating times. Due to the annealing, Ag or Au diffused into Si and/or Si diffused into the metal. The changes of the surface composition are analyzed by a quantitative Auger Electron Spectroscopy (AES) method which is newly developed as a non-destructive method. In the case of Ag/Si, Ag migrated into the Si substrate and/or Si diffused into Ag. Then, Ag-Si solid solution was produced. After the annealing, the Ag/Si system is changed into Ag/(Ag-Si)/Si of the three-phase structure. In the case of Au/Si (Au film thickness < 15 ,/k), the Au film thickness became thinner by annealing. The Au/Si system always keeps the Au/Si phase after annealing, while there was no Au-Si solution area. The difference between the Ag/(Ag-Si)/Si and the Au/Si structure is attributed to the reason that Au diffuses more quickly than Ag into the Si substrate. AES results after annealing cannot be explained by the model of the formation of the three-dimensional island structure which is commonly referenced.

Modifications of the surface reactivity of Ni(100) by structured overlayers of sulfur: Selectivity changes for ethanol and isopropanol decomposition

Download PDF Report

Upload
sw-johnson
View
214
Download
2

Embed Size (px)

Citation preview

Page 1: Modifications of the surface reactivity of Ni(100) by structured overlayers of sulfur: Selectivity changes for ethanol and isopropanol decomposition

A103

Surface Science 115 (1982) 61-78 Noi:th-Holland Publishing Company

M O D I F I C A T I O N S O F T H E S U R F A C E R E A C T I V I T Y O F Ni (100) B Y S T R U C T U R E D O V E R L A Y E R S O F S U L F U R : S E L E C T I V I T Y

C H A N G E S F O R E T H A N O L A N D I S O P R O P A N O L D E C O M P O S I T I O N

S.W. J O H N S O N * and R.J . M A D I X

Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA Received 7 July 1981; accepted for publication 28 October 1981

The reactions of ethanol and isopropanol were studied on Ni(100), Ni(100) p(2X2)S and Ni(100) c(2 X 2)S by temperature programmed reaction spectroscopy (TPRS). On both Ni(100) and Ni(100) p(2X2)S decomposition to adsorbed CO and atomic hydrogen dominated the reaction. Methane was also formed by the reaction of adsorbed hydrogen atoms with fragments of the decomposition, most likely carbon atoms. On ~ooth surfaces evidence for a COH complex was observed, similar to previous results with methanol. On Ni(100) c(2X2)S the selectivity of the reactions changed dramatically. Formation of aldehydes was enhanced at the expense of CO and H2; methane was not observed. From these results it appears that alkoxy intermediates formed on all three surfaces by dehydrogenation and that their further decomposition to CO, Hta ) and Cta) was limited by adsorbed sulfur.

Surface Science 115 (1982) 79-90 North-Holland Publishing Company

N E W S U R F A C E S T R U C T U R E A N A L Y S I S O F A g - S i P H A S E B Y

Q U A N T I T A T I V E A U G E R E L E C T R O N S P E C T R O S C O P Y M E T H O D

H. T O K U T A K A , K. N I S H I M O R I , S. N O M U R A , A. T A N A K A and

K. T A K A S H I M A

Department of Electronics, Faculty of Engineering, Tottori University, Koyama, Tottori, Japan Received 14 July 1981; accepted for publication 19 October 1981

Ag or Au was deposited on a clean Si substrate at room temperature. These systems, Ag/Si and Au/Si, were annealed at various temperatures or various heating times. Due to the annealing, Ag or Au diffused into Si and/or Si diffused into the metal. The changes of the surface composition are analyzed by a quantitative Auger Electron Spectroscopy (AES) method which is newly developed as a non-destructive method. In the case of Ag/Si, Ag migrated into the Si substrate and/or Si diffused into Ag. Then, Ag-Si solid solution was produced. After the annealing, the Ag/Si system is changed into Ag/(Ag-Si)/Si of the three-phase structure. In the case of Au/Si (Au film thickness < 15 ,/k), the Au film thickness became thinner by annealing. The Au/Si system always keeps the Au/Si phase after annealing, while there was no Au-Si solution area. The difference between the Ag/(Ag-Si)/Si and the Au/Si structure is attributed to the reason that Au diffuses more quickly than Ag into the Si substrate. AES results after annealing cannot be explained by the model of the formation of the three-dimensional island structure which is commonly referenced.