According to a study published on PNAS on Jan. 11, researchers led by Prof. HAO Zhengping from the University of Chinese Academy of Sciences (UCAS) have proposed a facile oxygen vacancy (V_O) engineering on titanium-based perovskite to motivate water (H₂O) activation, achieving enhanced organic sulfur hydrolysis and efficient sulfur recovery at lower temperature.

Water activation is a perennial topic involving many reactions and processes. Organic sulfur (COS and CS₂) hydrolysis is one such typical reaction involving H₂O molecule as a reactant. In industrial sulfur recovery process, an additional hydrolysis catalyst is installed in the first stage of the Claus reactor to convert COS and CS₂. Limited by effective activation of water, relatively higher temperature is required for the hydrolysis of CS₂ in complex environment, which is not conducive to the sulfur recovery reaction, thus severely affecting the sulfur recovery efficiency and pollution emission control of the Claus process.

In this study, the researchers fabricated titanium-based perovskites with different V_O contents, and found that there was a linear correlation between the V_O content and the degree of H₂O dissociation and hydrolysis performance. The low-coordinated Ti ions adjacent to V_O were active sites for H₂O activation.

The introduction of V_O, especially V_O clusters, resulted in the reduction of the energy barrier for H₂O dissociation, which contributed to H₂O activation and dissociation, according to the researchers.  

Furthermore, their in-depth mechanism study revealed that CS₂ hydrolysis was initiated from the reaction between dissociatively adsorbed -OH and gaseous CS₂ (Eley-Rideal mechanism), which was the origin of the enhanced hydrolysis activity from the enhanced H₂O activation by V_O.

Consequently, complete conversion of COS and CS₂ was achieved over SrTiO₃ after H₂ reduction treatment at 225 °C, a favorable temperature for the Claus conversion. Surprisingly, the catalyst also showed excellent Claus catalytic activity.

Thus, both efficient organic sulfur hydrolysis performance and improved sulfur recovery efficiency can be achieved simultaneously. The application of this dual-functional catalyst can significantly improve the sulfur recovery efficiency, simplify the operation process, and reduce the investment and operational cost.

Prof. HAO's team has long been engaged in the research and development of acid gas pollution control, resource recovery and utilization, and has in-depth understanding and thinking on acid gas emission reduction and control. The production and publication of the results are based on the team's work and accumulation over many years. The research results are of great significance to the emission reduction control, resource recovery and utilization of acid gas.

This work was supported by the National Natural Science Foundation of China, the Key R&D Program of Shandong Province, and the Fundamental Research Funds for the Central Universities. 

A schematic illustration for the comparison of traditional and novel operation process. (Image by UCAS)