Since the emergence of a novel coronavirus disease 2019 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported from Wuhan, China, neither a specific vaccine nor an antiviral drug against SARS-CoV-2 has become available. However, a combination of two HIV-1 protease inhibitors, lopinavir and ritonavir, has been found to be effective against SARS-CoV, and both drugs could bind well to the SARS-CoV 3C-like protease (SARS-CoV 3CL pro ). In this work, molecular complexation between each inhibitor and SARS-CoV-2 3CL pro was studied using all-atom molecular dynamics simulations, free energy calculations, and pair interaction energy analyses based on MM/PB(GB)SA and FMO-MP2/PCM/6-31G* methods. Both anti-HIV drugs interacted well with the residues at the active site of SARS-CoV-2 3CL pro . Ritonavir showed a somewhat higher number atomic contacts, a somewhat higher binding efficiency, and a somewhat higher number of key binding residues compared to lopinavir, which correspond with the slightly lower water accessibility at the 3CL pro active site. In addition, only ritonavir could interact with the oxyanion hole residues N142 and G143 via the formation of two hydrogen bonds. The interactions in terms of electrostatics, dispersion, and charge transfer played an important role in the drug binding. The obtained results demonstrated how repurposed anti-HIV drugs could be used to combat COVID-19.

The morphology effect of ZrO 2 −CeO 2 on the performance of MnO x /ZrO 2 −CeO 2 catalyst for the selective catalytic reduction of NO with ammonia was investigated. The catalytic tests showed that the MnO x /ZrO 2 −CeO 2 nanorods achieved significantly higher NO conversions than the nanocubes and nanopolyhedra. The catalytic tests also showed that the MnO x /ZrO 2 −CeO 2 nanorods achieved a significantly higher rate constant with respect to NO conversion than that of the nanocubes and nanopolyhedra. On the nanorods, the apparent activation energy is 25 kJ mol −1 , which was much lower than the values of nanocubes and nanopolyhedra (42 and 43 kJ mol −1 ). The high resolution transmission electron microscopy showed that the nanorods predominately exposed {110} and {100} planes. It was demonstrated that the ZrO 2 −CeO 2 nanorods had a strong interaction with MnO x species, which resulted in great superiority for the selective catalytic reduction of NO. The excellent catalytic activity of the MnO x /ZrO 2 −CeO 2 nanorods should be attributed to the Mn 4+ species, adsorbed surface oxygen and oxygen vacancies which are associated with their exposed {110} and {100} planes.

CeO 2 nanorods impregnated with 2.5 atom % of NiO (NiO/ CeO 2 nanorods) were successfully synthesized and examined as catalysts for the NH 3 -selective catalytic reduction (NH 3 -SCR) of nitric oxide (NO). The catalytic activity of NiO/CeO 2 nanorods resulted in up to ∼90% NO conversion at 250 °C, which is superior to that of pure CeO 2 nanorods or NiO nanoparticles. Subsequently, extensive studies of the NiO/CeO 2 -catalyzed reduction of NO were conducted using X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed desorption, and density functional theory periodic calculations. Compared to that of the pure CeO 2 nanorods, the results demonstrated that the NiO/CeO 2 nanorods resulted in (i) a higher concentration of Ce 3+ chemical species, (ii) a larger amount of active O α , (iii) lower temperature reducibility, (iv) a lower amount of energy required for oxygen vacancy distortion, and (v) a significant adsorption of and strong interaction between NO and NH 3 molecules. Our findings therefore elucidated considerable details of the structural properties of the NiO/CeO 2 nanorods that were decisive for achieving a highly efficient conversion of NO by the NH 3 -SCR process at low temperatures.

Manganese oxides (MnO x ) supported on Ce 0.9 Zr 0.1 O 2 (MnO x /Ce 0.9 Zr 0.1 O 2 ) nanorods were synthesized and tested for lowtemperature selective catalytic reduction of NO with ammonia. The catalysts were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed reduction. The structure and morphology results show that the MnO x was highly dispersed on the surface of Ce 0.9 Zr 0.1 O 2 nanorods. Various species, such as Mn 2+ , Mn 3+ , and Mn 4+ , were exposed due to a strong interaction between manganese and cerium oxides. Thus, the MnO x /Ce 0.9 Zr 0.1 O 2 nanorods exhibited a better catalytic performance (90% NO conversion at 150 °C) compared with that of the as-prepared Ce 0.9 Zr 0.1 O 2 nanorods. Density functional theory (DFT) calculations clearly demonstrated that the MnO x on the surface of supporting nanorods or Mn@ CeO 2 (110) could easily form an oxygen vacancy distortion. Furthermore, the Mn@CeO 2 (110) model in the DFT analysis showed a prominent effect on the NO and NH 3 adsorption which resulted in a stronger nitrite intermediate (NOO*) formation and more attractive interaction with the NH 3 gas compared with those observed with the CeO 2 (110) model. Therefore, a thorough understanding of the structure and catalytic performance of MnO x /Ce 0.9 Zr 0.1 O 2 nanorods was successfully achieved by a combination of experimental and theoretical studies.

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