Supplementary information
Size effects in Atomic-Level Epitaxial Redistribution Process of RuO2
over TiO2
Guolei Xiang2, Xuejun Shi1, Yulong Wu1*, Jing Zhuang2 and Xun Wang2*
1 Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, P. R.
China
2 Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China
G. L. X. and X. J. S. contributed equally to this work.
E-mail: wangxun@mail.tsinghua.edu.cn; wylong@tsinghua.edu.cn
Figure S1. The equilibrium conversion percentages of HCl as the functions of temperature and the
feed ratios of HCl. a, line data. b, 2D profile. The right inset shows the conversion varied with
temperature at 0.2 feed ratio of HCl; the top inset is the conversion of HCl at 300 oC with different
HCl feed ratios.
a
b
With regard to the gas-phase oxidation reaction of HCl with O2, nearly all the patented and
experimental reports were derived from Deacon process, as represented by the following reaction
Cata .

 2Cl2 (g)+2H 2O(g)+116.4kJmol-1
4HCl  g  +O 2  g  

The reaction is a reversibly exothermic process, with a reaction enthalpy change of 116.4 kJmol -1
at 573 K. To realize economically industrial run, high temperatures are usually required to increase
the total reaction rates, but simultaneously reducing the equilibrium conversion of HC1. Arnold and
Kobe clarified the equilibrium conditions for this process.18 They fitted the correlation of equilibrium
constant (Ke) with reaction temperature as the following equation
lg K e  5881.7 / T - 0.93035lg T  1.37014 10-4 T -1.758110-8 T 2 - 4.1744
（pH 2O / p ) 2 ( pCl2 / p ) 2
Ke 
( pHCl / p ) 4 ( pO2 / P )
According to the above equations, the equilibrium conversions of HCl, as the function of
temperature ranging from 200 oC to 600 oC and the feed ratio of HCl, are calculated as diagramed in
Figure S1. It can be seen that the theoretic conversion percentage of HCl decreases rapidly with the
increase of reaction temperature. A relatively higher conversion above 90% can be realized below
300 oC with lower HCl feed ratios. To realize both high conversion rate and production efficiency in
industrial runs, the operation temperatures are usually set ranging from 350 oC to 600 oC. Aiming at
optimizing the most suitable operation conditions for industrial practice, here we investigate the
reaction at 300 oC with HCl feed ratio of 20% (the total pressure is 1 bar).
Figure S2. TEM images show the surfaces of H-P25-TiO2 after 72-h Deacon reaction.
a
b
c
Figure S3. TEM results of RuO2/P25-TiO2 catalyst prepared via impregnation method at 400 oC.
Figure S4. The theoretical model based on interface tensions to analyze the stability of
heteroepitaxial particles on substrates.
The diagram illustrates the epitaxial structure of spherical particle grown on a substrate, in which
the angle θ is the contact angle between the particle and the substrate. The parameters r and h
represent the radius and the height of the spherical crown particle, respectively. The interface area of
boundary is AI   (r sin  ) 2 ; the surface area of the crown is Ac  2 r 2 (1  cos  ) ; the volume of the
 r3
V

(1  cos  ) 2 (2  cos  )
c
crown is
3
.
For a spherical particle deposited on a substrate, there are three interfacial tensions determining its
thermodynamic equilibrium shape. They are denoted as γe (between the epilayer and air), γs (between
the substrate and air) and γs-e (between the interface of substrate and the epilayer). Under equilibrium
conditions, the forces are balanced in the horizontal direction as expressed by Young’s Equation
 e cos    s   s e
At a certain temperature when the atoms can overcome the constraints from the lattice by
acquiring enough vibration energy from the environment, catalyst particles will become instable by
leaching atoms into the environment or undergoing shape change due to surface relaxation. In an
equilibrium phase or shape transition process, the free energy change ΔG can be expressed as22,36
G  Vc G v  AI ( s   s e )  Ac e
 r 3Gv
(1  cos  ) 2 (2  cos  )   ( r sin  ) 2  e cos   2 r 2 (1  cos  ) e
3
 r 3Gv
(
  r 2 e )(1  cos  ) 2 (2  cos  )
3
4 r 3 Gv
(
 4 r 2 e ) f ( )
3

f ( )  (1  cos  )2 (2  cos  ) / 4
where
Vc G v =
 r 3Gv
3
(1  cos  ) 2 (2  cos  )
is
the
overall
free
energy
increase;
- Ac e =  2 r 2 (1  cos  ) e is the overall free energy decrease resulted from the vanishment of
surface and  (r sin  ) 2  e cos  is the free energy change due to the transformation of boundary.