Oxidative coupling of toxic pollutant CO to form the platform raw chemical material dimethyl oxalate (DMO) has been industrialized however the catalytic mechanism has been unknown so far. The reaction mechanism of CO oxidative coupling to form DMO on a Pd(111) surface has been investigated using density functional theory (DFT) and in situ diffuse reflectance infrared (DRIR) spectroscopy. DFT calculations and in situ DRIRS measurements indicate that two co-adsorbed intermediates COOMe and OCCO, initiate the reaction. C-C coupling occurs earlier due to a low coupling barrier and small steric hindrance. The results also suggest that Pd(111) is selective towards DMO over DMC, and that CO pre-adsorption and CO in excess effectively enhance the yield of DMO. The microscopic elucidation of this important reaction suggests improvements in coal-to-EG (CTEG) production which can be applied in practice to effectively enhance the yield and reduce the cost. The results may help with further fine-tuning and designing of high-efficient noble metal catalysts.
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.
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