Zinc oxide (ZnO), with the unique chemical and physical properties of high chemical stability, broad radiation absorption range, high electrochemical coupling coefficient, and high photo-stability, is an attractive multifunctional material which has promoted great interest in many fields. What is more, its properties can be tuned by controllable synthesized morphologies. Therefore, after the success of the abundant morphology controllable synthesis, both the morphology-dependent ZnO properties and their related applications have been extensively investigated. This review concentrates on the properties of morphology-dependent ZnO and their applications in catalysis, mainly involved reactions on green energy and environmental issues, such as CO₂ hydrogenation to fuels, methanol steam reforming to generate H₂, bio-diesel production, pollutant photo-degradation, etc. The impressive catalytic properties of ZnO are associated with morphology tuned specific microstructures, defects or abilities of electron transportation, etc. The main morphology-dependent promotion mechanisms are discussed and summarized.

The performance of plasma-modified Pt/CeO₂ for toluene catalytic oxidation was investigated. Pt/CeO₂ nanorods were prepared by wet impregnation and were modified by thermal (PC-T), plasma (PC-P), and combined (PC-TP and PC-PT) treatments. The modified catalysts were characterized by TEM (transmission electron microscope), BET (Brunauer-Emmett-Teller), H₂-TPR, O₂-TPD, XPS, UV-Raman, and OSC tests. The significant variation of the surface morphologies and surface oxygen defects could have contributed to the modification of the Pt/CeO₂ catalysts via the plasma treatment. It was found that plasma could promote the surface interaction between Pt and CeO₂, resulting in the thermal stability of the catalyst. The Pt-Ce interaction was also conducive to an increase in the number of oxygen vacancies. Furthermore, PC-PT and PC-TP showed a significant difference in oxygen vacancy concentrations and catalytic activities, which illustrated that the treatment sequence (plasma and thermal treatment) affected the performance of Pt/CeO₂. The PC-PT sample showed the highest catalytic activity with T₁₀₀ at 205 °C. This work thus demonstrates that plasma in combined treatment sequences could assist surface interactions of catalysts for enhanced toluene catalytic oxidation.

CO₂ hydrogenation to methanol is one of the main and valuable catalytic reactions applied on Cu/ZnO-based catalysts; the interface formed through Zn migration from ZnO support to the surface of Cu nanoparticle (ZnOx-Cu NP-ZnO) has been reported to account for methanol synthesis from CO₂ hydrogenation. However, the accompanied reverse water gas shift (RWGS) reaction significantly decreases methanol selectivity and deactivates catalysts soon. Inhibition of RWGS is thus of great importance to afford high yield of methanol. The clear understanding of the reactivity of RWGS reaction on both the direct contact Cu-ZnO interface and ZnOx-Cu NP-ZnO interface is essential to reveal the low methanol selectivity in CO₂ hydrogenation to methanol and look for efficient catalysts for RWGS reaction. Cu doped plate ZnO (ZnO:XCu) model catalysts were prepared through a hydrothermal method to simulate direct contact Cu-ZnO interface and plate ZnO supported 1 wt % Cu (1Cu/ZnO) catalyst was prepared by wet impregnation for comparison in RWGS reaction. Electron paramagnetic resonance (EPR), XRD, SEM, Raman, hydrogen temperature-programmed reduction (H₂-TPR) and CO₂ temperature-programmed desorption (CO₂-TPD) were employed to characterize these catalysts. The characterization results confirmed that Cu incorporated into ZnO lattice and finally formed direct contact Cu-ZnO interface after H₂ reduction. The catalytic performance revealed that direct contact Cu-ZnO interface displays inferior RWGS reaction reactivity at reaction temperature lower than 500 °C, compared with the ZnOx-Cu NP-ZnO interface; however, it is more stable at reaction temperature higher than 500 °C, enables ZnO:XCu model catalysts superior catalytic activity to that of 1Cu/ZnO. This finding will facilitate the designing of robust and efficient catalysts for both CO₂ hydrogenation to methanol and RWGS reactions.