Li Gao, research group of Dalian Institute of Chemical Sciences: Ti doped CeO 2 tixce1-xo2 nanocomposites for efficient green catalytic synthesis of dimethyl carbonate

Dimethyl carbonate (DMC), a green chemical with high oxygen content, can be used as a fuel oil additive to increase octane number, improve combustion efficiency and reduce exhaust emissions In addition, DMC is a very important raw material in the chemical synthesis process, which can produce methylation and carbonylation reactions Based on this, the synthesis of DMC has important economic value and practical application value At present, the main methods of DMC synthesis are transesterification, phosgene, urea alcoholysis, methanol oxidative carbonylation, and direct synthesis with CO2 and CH3OH Each method has its own advantages and disadvantages, for example, the raw material of phosgene method is highly toxic, the raw material of direct synthesis method methanol and CO2 are cheap, but it is not feasible in the field of thermodynamics, and the yield is extremely low In recent years, how to improve the yield of this simple, nontoxic and green synthesis method has great significance and challenges Recently, the research group of Li Gao, researcher of Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has made a new breakthrough in this field, and the relevant results are published online in green chem (DOI: 10.1039 / c9gc00811j) Li Gao, researcher, State Key Laboratory of catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences Graduated from Hunan Normal University in 2004 In 2011, he received his doctorate in Applied Chemistry from Shanghai Jiaotong University From 2011 to 2014, he worked as a postdoctoral researcher at Carnegie Mellon University In 2014, he joined Dalian Institute of Chemical Physics, and in 2015, he won the support of "thousands of young people" He has published more than 80 papers in high-level magazines such as JACS, nature commun, angelw, etc The research direction is: synthesis and catalysis of metal clusters Cutting edge scientific research achievements: Ti doped CeO 2 Ti x CE 1-x O 2 nanocomposites can catalyze the synthesis of dimethyl carbonate by direct reaction of carbon dioxide and methanol to DMC The raw materials of the reaction are widely available, the cost is low, and no toxic and harmful substances are produced in the reaction process However, due to the limitation of thermodynamic equilibrium and the high chemical inertness of carbon dioxide molecules, the reaction is usually carried out in a autoclave, so that the by-product water can not be removed in time, making the reaction yield very low Because of its large specific surface area and high oxygen storage capacity, CeO 2 has good activity in the direct synthesis of DMC by CO 2 and methanol However, its stability was poor, and its activity decreased rapidly with the increase of the number of cycles (10 h) In this paper, Ti x CE 1-x O 2 nanocomposites were synthesized by Ti doped ceria to form a whole catalyst for direct synthesis of DMC The monolithic catalyst has the advantages of large specific surface area, small pressure drop, excellent mechanical properties and good thermal stability In addition, the reaction products (water and DMC) can be removed in time to improve the catalytic efficiency The results show that the surface oxygen vacancy concentration is increased by Ti doping In the absence of any dehydrating agent, Ti dopant makes the conversion of the reaction 24.3% and the selectivity 78.6% at 140 ℃ (Fig 1) Fig 1 Synthesis of dimethyl carbonate (source: Green Chem) by Ti doped ceria Ti x CE 1-x O 2 nanocomposites with high efficiency and green catalysis Firstly, the catalysts with different Ti and CE ratios were synthesized by adjusting the ratio of (NH 4) 2ce (NO 3) 6 and Ti (so 4) 2 raw materials, and were characterized and compared by XRD and Raman After Ti doping into CeO 2, the (111) diffraction peak widens and shifts to a high angle, which indicates that Ti doping is successful and the lattice of CeO 2 shrinks The 604cm-1 band in the Raman spectrum is attributed to the intrinsic oxygen vacancy With the increase of Ti concentration, the stronger the intrinsic oxygen vacancy is, indicating that Ti XCE 1-xo 2 nanocomposites have high potential for DMC synthesis (Fig 2) Fig 2 A) XRD, b) local amplification and C) Raman spectra of Ti doped CEO 2-ti-x-ce 1-x-o 2 nanocomposites (source: Green chem.) then, the oxidation states of CE, Ti and O on the surface were characterized by XPS They found that the ratio of Ce3 + to CeO2 is 3.33%, Ti in the complex shows the only positive tetravalent, while o has three forms: lattice oxygen (529.3ev), vacancy oxygen (530.5ev) and adsorbed oxygen (532.2ev) After doping Ti, the ratio of vacancy oxygen to adsorbed oxygen increases, and compared with different x values, Ti 0.1 CE 0.9 O 2 has the highest capacity of adsorbing carbon dioxide and storing oxygen (Fig 3) Fig 3 XPS energy spectrum and analysis fitting results of Ti doped CeO 2 Ti x CE 1-x O 2 nanocomposites (source: Green Chem) The author applied Ti doped CeO 2 Ti x CE 1-x O 2 nanocomposites to the direct synthesis of DMC, and investigated the conversion rate of these catalysts in this reaction At 140 ℃ and CH3OH: CO2 = 2.0:1.0 (V / V), Ti 0.1 CE 0.9 O 2 showed the highest methanol conversion, up to 24.3% Ti 0.1 CE 0.9 O 2 has the highest yield and the highest concentration of active site These results show that Ti (x = 0.1) with the best doping concentration in the CeO 2 lattice can make the concentration of active surface sites the highest, thus promoting the synthesis of direct DMC The stability of the catalyst was also studied by the research team Within 10 hours, the conversion of methanol and the selectivity of DMC were almost unchanged, which were ~ 25% and ~ 78%, respectively After 48 hours of reaction, the conversion and selectivity of the catalyst decreased slightly, which were 20.6% and 74% respectively, which was related to the surface coverage of the catalyst by the carbonate species produced in the reaction In order to test the recoverability of the catalyst, the Ti 0.1 CE 0.9 O 2 catalyst after reaction was recovered and annealed in air at 350 ℃ for 3 h to eliminate any potential surface molecules After six cycles, the catalytic activity did not decrease significantly, indicating that the Ti x CE 1-x O 2 nanocomposite catalyst has a good application prospect for the direct synthesis of DMC (Fig 4) Figure 4 Catalytic reaction of Ti doped CeO 2 / Ti x CE 1-x O 2 nanocomposites (source: Green chem.) Summary: the author synthesized Ti doped CeO 2 nanocomposites by coprecipitation method, and studied the catalytic activity of the composite for direct synthesis of DMC by CO 2 and CH 3OH Among them, Ti 0.1 CE 0.9 O 2 has the highest activity, the conversion of Ch 3OH is 24.3%, and the selectivity of DMC is 79% The results of XPS and Raman analysis show that the catalytic performance of Ti XCE 1-xo 2 composite is related to the oxygen vacancy concentration and the type of chemisorption oxygen In order to overcome the limitation of kinetics and thermodynamics, the strategy of designing a continuous reaction platform under heterogeneous catalysis was put forward This work was published in greenchem (DOI: 10.1039/c9gc00811j) under the title of "Ti x CE 1-x O 2 nanocomposites: a monolithiccatalyst for direct conversion of carbon dioxide and methanol to dimethylcarbon" (author: Yongdong Chen *, Hong Wang, Zhaoxian Qin, Shanli Tian, Zhongbin ye, Lin Ye, Hadi abroshan * and Gao Li *) Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit