Zhongming Wang,Hang Yuan,Siting Chen,Yong Jia,Lina Guo,Hong Wang,Wenxin Dai
The progressive transfer of photogenerated electrons between the catalyst components and reactants is of great significance for photocatalysis. Amorphous Pd (Pd A ) and oxygen vacancies (V O s) were simultaneously introduced in Pd-In 2 O 3 exploiting hydrogen-induced amorphization effects; 0.6 wt% Pd-In 2 O 3 exhibited a 4.5-fold increase in activity and a 3.2-fold higher selectivity toward CH 3 OH + CO (63.62 %) compared with In 2 O 3 . Multiple in situ techniques and theoretical calculations revealed that intercomponent electron transfer channels were established via various interface structures formed between Pd A or crystalline Pd (Pd C ) and In 2 O 3 ; Pd A acted as electronic pump, facilitating the transfer and separation of photogenerated electrons, resulting in their subsequent enrichment on the surface of Pd A . Simultaneously, Pd A acted as electron-donating adsorption site for H 2 O, increasing the number of electrons received by H 2 O, further inhibiting the competitive adsorption of H 2 O and CO 2 on V O sites, and promoting the hydrogen evolution reaction. Additionally, the electronic coupling between Pd C and V O s could significantly decrease the electron-donating ability of V O s, reducing the number of electrons received by CO 2 , thus effectively regulating the degree of CO 2 reduction. This study employs Pd A /Pd C and V O s to synergistic optimize the progressive transfer of photogenerated electrons, and presents a novel approach for elucidating the catalytic mechanism.
Gas sensors based on In 2 O 3 were prepared and were found to be very sensitive to methane with Pd loading (Pd-In 2 O 3 ), even at a low temperature of 300 °C. However, Pd-In 2 O 3 sensors suffer from a high cross-sensitive response to NO 2 , CO and ethanol, which are typical interfering gases for the detection of CH 4 . In order to promote the selective response to CH 4 , a filter based on Pt-Al 2 O 3 catalyst film was printed onto the top of Pd-In 2 O 3 sensor layer. It was found that catalytic film coated sensors could selectively respond to methane even in the mixture of methane with CO, NO 2 , and ethanol. The cross-sensitive responses to the interference of VOCs, CO, NO 2 were almost eliminated. According to the catalytic conversion measurement, it was indicated that CO and ethanol were fully and selectively oxidized to CO 2 and H 2 O. In case of NO 2 , it was proposed that nitrogen dioxide molecules may be blocked on the surface of the catalyst film. Based on the oxygen adsorption behavior, it was suggested the printed catalyst film has no change on the basic sensing mechanism of In 2 O 3 based sensors following the general model that is the adsorption of oxygen and interaction with methane molecule and the resulted electron transfer process. Our investigation demonstrated that Pt-Al 2 O 3 printed Pd-In 2 O 3 sensor could be used for the detection of CH 4 leakage and monitor.
The nitrite (NO 2 − ) to ammonia (NH 3 ) electroreduction reaction (NO 2 − RR) would be impeded by sluggish proton-coupled electron transfer kinetics and competitive hydrogen evolution reaction (HER). A key to improving the NH 3 selectivity is to facilitate adsorption and activation of NO 2 − , which is generally undesirable in unitary species. In this work, an efficient NO 2 − RR catalyst is constructed by cooperating Pd with In 2 O 3 , in which NO 2 − could adsorb on interfacial dual-site through “Pd–N–O–In” linkage, leading to strengthened NO 2 − adsorption and easier N=O bond cleavage than that on unitary Pd or In 2 O 3 . Moreover, the Pd/In 2 O 3 composite exhibits moderate H* adsorption, which may facilitate protonation kinetics while inhibiting competitive HER. As a result, it exhibits a fairly high NH 3 yield rate of 622.76 mmol h −1 g −1 cat with a Faradaic efficiency (FE) of 95.72%, good selectivity of 91.96%, and cycling stability towards the NO 2 − RR, surpassing unitary In 2 O 3 and Pd/C electrocatalysts. Besides, computed results indicate that NH 3 production on Pd/In 2 O 3 follows the deoxidation to hydrogenation pathway. This work highlights the significance of H* and NO 2 − adsorption modulation and N=O activation in NO 2 − RR electrochemistry by creating synergy between a mediocre catalyst with an appropriate cooperator.
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