EDITORIAL

CHINESE JOURNAL OF CATALYSIS Volume 28, Issue 11, November 2007 Online English edition of the Chinese language journal

Cite this article as: Chin J Catal, 2007, 28(11): II–V.

Copyright © 2007, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved.

Gerhard Ertl and His Research with Surface Science

On October 10 the Royal Swedish Academy of Sciences announced that Professor Gerhard Ertl of the Fritz Haber In-stitute of the Max Planck Society, Germany was awarded the 2007 Nobel Prize in chemistry for his groundbreaking studies of chemical processes on solid surfaces.

Prof. Ertl was born in Germany in 1936 and received his PhD from Technical University of Munich in 1965. After working at Technical University of Hannover and at Ludwig Maximilians University of Munich, he became the director of Fritz Haber Institute of the Max Planck Society in 1986. He is now an emeritus professor of this institute. Since 1997, he has been a member of the advisory board of the Chinese Journal of Catalysis.

Prof. Ertl worked in many research fields, including surface catalysis and electrochemistry, where he has made many breakthroughs. The most important contribution is perhaps his studies of chemical processes on solid surfaces, which was cited in the prize announcement by the Royal Swedish Academy of Sciences. It was due to processes developed in the semiconductor industry that modern surface science began to emerge in the 1960s. Prof. Ertl was one of the first to rec-ognize the potential of these new techniques for studies of molecular processes at surfaces. He created a general method-ology that can be applied to the study of the chemistry on solid surfaces. His work demonstrated how the combination of many different experimental techniques can be used to provide a complete picture of a surface reaction at the atomic and molecular scales. His efforts laid a scientific basis for modern surface chemistry. The methodology he developed is now widely applied in both academic research and industrial development of chemical processes. The studies on the reac-tion mechanism of the Haber–Bosch process and the oxidation of carbon monoxide on platinum are the two most important contributions from Prof. Ertl.

1 Surface science and Haber–Bosch process

The Haber–Bosch process is one of the most important het-erogeneous catalytic processes. In this process, nitrogen that is separated from air reacts with hydrogen to form ammonia. The invention of iron-based catalysts for ammonia synthesis opened a new era for both the modern chemical industry and

modern agriculture. Prof. Ertl used various surface techniques to study systematically the Haber–Bosch process on model catalysts. He found that the active species are adsorbed atomic nitrogen and hydrogen, the dissociation of nitrogen molecules on the surfaces is the limiting step, and dissociated nitrogen atoms react with hydrogen atoms to form ammonia by ob-serving all reaction intermediates. Furthermore, he provided the energy potential of each step in the reaction (Fig. 1).

Fig. 1 An energy diagram showing the progression of reaction from the reactants N2 and H2 to the product NH3. Energies are given in units of kJ/mol. From G. Ertl, J Vac Sci Technol A, 1 (1983) 1247.

Prof. Ertl used electron spectroscopic techniques to analyze the surface composition of commercial catalysts and study the variation of the surface nitrogen coverage with changing hy-drogen pressures during the reaction. The results under high pressures were consistent with that obtained on model cata-lysts at low pressures. This indicated that the results on model catalyst surfaces can be extended to the commercial catalysts. His research on the Haber–Bosch process has become a model for how modern surface science techniques can be combined to study and understand the surface chemistry of complex heterogeneous catalytic processes.

2 CO oxidation and non-linear reaction dynamics

The catalytic oxidation of CO on platinum is one of the main reactions needed to clean car exhaust gases. Prof. Ertl conducted systematic investigations on a model catalyst for this reaction and founded the theory of non-linear kinetics of

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surface reactions. In 1982, his research group first reported a non-linear reaction dynamic behavior in CO oxidation on Pt single crystals. The rate of CO2 formation oscillated with re-action time (Fig. 2). The study of the dependence of the CO oxidation rate on the concentration of reactive species on Pt and the surface structure of Pt single crystals established a microscopic model for the non-linear reaction behavior of CO oxidation on the Pt single crystal surface.

Fig. 2 Kinetic oscillations in catalytic CO oxidation on Pt(110) measured via the variation of the CO2 partial pressure pCO2,CO partial pressure pCO, and the Pt surface work function variation. From R. Imbihl and G. Ertl, Chem Rev, 95 (1995) 697.

Additionally, the surface reactions are dependent on the spatial scale at the catalyst surfaces. Thus, the oscillating re-actions will exhibit characteristic patterns as a function of time and space. In order to see the reaction patterns, his group developed photoemission electron microscopy (PEEM) that enabled in situ studies on the concentration of the adsorbed species on the catalyst surface at pressures < 10 4 mbar (time and spatial resolutions are ms and sub- m, respectively). They observed rich adsorption patterns originating from the spatial organization of CO and O2 domains on the surface that changed from spiral to chaos patterns (Fig. 3). These results provided profound insights of the reaction dynamics on solid surfaces.

3 The status of research on surface chemistry in China

In the 1930s, Professor Zhang Dayu started scientific re-search on colloidal chemistry and surface chemistry in China after his PhD at Technical University of Dresden. In the 1950s he moved on to the studies on commercially used catalysts.

Based on the research on catalytic reactions such as syngas conversion to fuels on cobalt-based catalysts and ammonia synthesis on iron-based catalysts, he established a series of research methods for physical and chemical adsorption and proposed a theory of surface bonding. Based on this theory, Prof. Zhang developed three catalysts for ammonia synthesis that showed superior catalytic performances. In addition, an-other two important contributors to surface chemistry research were Prof. Guo Xiexian of Dalian Institute of Chemical Phys-ics (DICP) and Prof. Deng Jingfa of Fudan University. Prof. Guo conducted a wide range of studies on surface catalysis and put forward many important concepts, such as the effect of surface vacancies on adsorption and reaction, synergetic effect and exchange reactions of adsorbed CO and H2. Prof. Deng designed and assembled many modern spectrometers in his laboratory and carried out systematic research on adsorp-tion and catalysis on surfaces, especially on Ag catalysts at the molecular level.

Fig. 3 Platinum surface imaged by photoemission electron micros-copy. Dark areas are rich in CO while light areas are O2 rich. Time scale ~10 s, length scale ~ 0.1 nm. From the surface imaging group, department of physical chemistry, Fritz- Haber Institute of the Max Planck Society, www.fhi-berlin. mpg.de/surfimag.

4 Prof. Ertl’s activity and involvement in the re-search of surface science and catalysis in China

Prof. Ertl has made significant contributions to the devel-opment of surface chemistry in China. Since 1997 he has been a member of the advisory board of the Chinese Journal of Catalysis. In 2000 he consented to be one of the international advisors for the State Key Laboratory of Catalysis in DICP, Chinese Academy of Sciences (CAS). He maintains close collaboration between his group and several Chinese research

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institutions including DICP and Xiamen University. More than 10 Chinese scientists have worked for extended periods in Prof. Ertl’s group. Prof. Bao Xinhe of DICP is one of them. He worked with Prof. Ertl between 1989 and 1995. Before he returned to China, Prof. Bao discussed with Prof. Ertl about

studying surface catalysis involving nanosized catalyst sys-tems and the understanding of the nanosize effects in hetero-geneous catalysis with the help of advanced nanoprobe tech-niques. Prof. Ertl appraised the idea and donated a PEEM setup his group had developed to support Prof. Bao’s research on surface and interface catalysis in China. In addition, Prof. Ertl initiated and helped to launch a CAS-MPG partner group on nanocatalysis, which is presently directed by Prof. Bao in China and Prof. Schloegl in Germany. Prof. Ertl himself took on the duty of the chairman of the scientific committee and he has spent three visits to the partner group in Dalian in the past 5 years (Fig. 4).

The continuous support and help that Prof. Ertl has given to the development of surface chemistry in China and to Chinese scientists are highly appreciated. Prof. Ertl is a distinguished scientist and also an excellent manager. We sincerely hope that more achievements will be made in the field of surface chemistry and catalysis in China with the support and help of Prof. Ertl.

HUANG Weixin Department of Chemical Physics, University of Science and Technology of China, China

FU Qiang State Key Laboratory of Catalysis, Dalian

Institute of Chemical Physics, Chinese Academy of Sciences, China

Fig. 4 Visit of Prof. Ertl to DICP in 2004 for the review of the CAS-MPG partner group on nanocatalysis directed by Prof. Bao Xinhe in China and listening to the report from Prof. Bao, the Associate Editor-in-Chief of the Chinese Journal of Catalysis (left)