Machida Masato
Department of Applied Chemistry and Biochemistry, Graduate School of Science and Technology Kumamoto University, 2-39-1 Kurokami, Chuo, Kumamoto, 860-8555, Japan.
Unit of Elements Strategy Initiative for Catalysts & Batteries Kyoto University, 1-30 Goryo-Ohara, Nishikyo, Kyoto 615-8245, Japan.
Chem Rec. 2016 Oct;16(5):2219-2231. doi: 10.1002/tcr.201600037. Epub 2016 Jun 1.
Metal phosphates stabilize Rh nanoparticles on their surface via Rh-O-P bonds, in contrast to the Rh-O-M bonds formed on metal oxides (MO ). The local structure, electronic structure, and redox properties of Rh nanoparticles anchored on metal phosphates, and their practical impacts on catalysis, are reviewed based on recent publications from the author's research group. Because of the covalency of the Rh-O-P bond, Rh oxide is readily reduced to metallic Rh having a higher catalytic activity, whereas Rh oxide on metal oxide supports is more difficult to reduce with an increase of the anchoring strength. Furthermore, Rh metal shows a higher tolerance to reoxidation when supported on metal phosphates because the Rh-O-P bond is preserved under reducing atmospheres. The electron deficiency of Rh metal is another feature that affects its catalytic properties, and the extent of the electron deficiency can be tuned by replacing the metal in the metal phosphate with one of higher basicity. Further impacts on practical performance (thermal stability, poisoning stability, and lean NO purification) in automobile catalyst applications are also described.
金属磷酸盐通过Rh-O-P键在其表面稳定铑纳米颗粒，这与在金属氧化物（MO）上形成的Rh-O-M键不同。基于作者研究小组最近的出版物，对锚定在金属磷酸盐上的铑纳米颗粒的局部结构、电子结构和氧化还原性质及其对催化的实际影响进行了综述。由于Rh-O-P键的共价性，氧化铑很容易还原为具有更高催化活性的金属铑，而金属氧化物载体上的氧化铑随着锚定强度的增加更难还原。此外，当负载在金属磷酸盐上时，铑金属对再氧化表现出更高的耐受性，因为Rh-O-P键在还原气氛下得以保留。铑金属的电子不足是影响其催化性能的另一个特征，通过用碱性更高的金属取代金属磷酸盐中的金属，可以调节电子不足的程度。还描述了对汽车催化剂应用中实际性能（热稳定性、抗中毒稳定性和贫燃NO净化）的进一步影响。
