Rh substituted-La 2 B 2 O 7 (B = Zr or Ti) composite oxides were synthesized and applied in the dry reforming of methane (DRM) reaction. The characterizations of XRD, Raman, UV−vis diffuse reflectance, HRTEM, HAADF-STEM, in situ DRIFTS, XAFS XPS, TPR and the tests of DRM reaction have shown that the degree of substitution and the catalytic performance depend on the composition of La 2 B 2 O 7 (B = Zr or Ti). It is found that almost all Rh species substituted Zr over the compact Rh-LZO while a part of Rh substituted Ti, and the rest existed in the form of Rh 2 O 3 on the surface over the loose Rh-LTO. CH 4 was prone to dissociate on Rh−La 2 Zr 2 O 7 but hard to continue owing to the quickly depositing of intermediate carbon, which would not be resolved unless enough active O* was furnished. On the other hand, titanium-doped La 2 Ti 2 O 7 conferred unique structural and charge effects to supported Rh through the metal−support interface, leading to the coexistence of Rh 0 and Rh δ+ which performed synergistically during DRM at 800 °C. We proposed that CH 4 would be activated on Rh sites continuously if generated carbon could be promptly oxidized by active O* species that originated from CO 2 dissociation. The coexistence of Rh 0 and Rh δ+ in Rh−La 2 Ti 2 O 7 facilitated the electron transfer and thus accelerated the mobility of active oxygen species, which could be proved by the variations of binding energy in Ti, O, and Rh.
The NaY zeolites were prepared by hydrothermal synthesis method. The influence of NaY zeolite calcined at different temperatures as carriers for Rh/NaY catalysts on the hydroformylation of formaldehyde was investigated. The physical and chemical properties of Rh/NaY catalysts and their performance were characterized in details. When the zeolites were calcined at 400-700 °C, the crystal structure and morphology were kept unchanged within this range of calcination temperature. However, the surface crystallinity and surface area were reduced with increasing the temperature due to the partially collapsed of its framework, and thus reducing the confine of cages structure to rhodium species promote its participation in the coordination reaction. The reduction in the amount of surface Lewis acid can reduce the electronegativity of the carrier and change the electronic state of the surface rhodium species, which would weaken the hindrance to anionic speciation and promote CO insertion, which facilitates the hydroformylation of formaldehyde.
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