In-situ growth of defect-enriched NiO film on nickel foam (NF@NiO) monolithic catalysts for ozonation of gaseous toluene

Engineering the Crystal Facet of Monoclinic NiO for Efficient Catalytic Ozonation of Toluene

“…This result was inconsistent with those previously reported; i.e., NiO with more Ni vacancies tended to generate more O vacancies. 21,22 A reasonable explanation was that the effect of Ni vacancies on the O-vacancy formation ability of the (110) facet was different from those of the (100) and (111) facets, which was well evidenced by H 2 -TPR, XPS, Raman analyses, and following DFT calculations (Figure 3, Figures S22−S24, and Table S2). S3.…”

“…21,22,29−34 Among these, crystal facet engineering has been highlighted as a promising strategy because different crystal facets of NiO have their own atomic arrangement patterns and thus distinctive electronic structure, which is believed to result in differences in Ni vacancies and thus dramatically influence O-vacancy formation. For example, Tian's group 22 by Zhan et al 21 has also shown that the high density of surface O vacancies generated in hydrochloric acid-modified cubic NiO might be due to the abundance of Ni vacancies in its exposed minor (111) facet, which promotes ROS formation and thus provides superior performance for CTO. However, the catalytic activity of cubic NiO remained unsatisfactory when it was used for CTO at room temperature.…”

“…However, the catalytic activity of cubic NiO remained unsatisfactory when it was used for CTO at room temperature. 21,22 Recently, monoclinic NiO has been found to exhibit superior catalytic activity at low temperatures or room temperature in several catalytic systems, such as methane and glycerol reforming, 35−37 phenol oxidative polymerization, 38 and ozone decomposition. 29 Inspired by these developments, we speculated that monoclinic NiO catalysts with specific exposed facets could show excellent activity for CTO at room temperature.…”

“…A widely recognized and accepted point is that reactive oxygen species (ROS) derived from ozone conversion on oxygen (O) vacancies play an important role in catalytic toluene ozonation (CTO). − Accordingly, a series of O-vacancy-enriched metal-based catalysts, including NiO x , , MnO x , , CuO x , PtO x , , and their derived composites, have been examined to achieve efficient CTO. Among these, nickel oxide (NiO) has received an enormous amount of attention due to its low cost, environmental friendliness, and excellent performance for CTO under mild conditions. , It is generally acknowledged that Ni vacancies, as a type of important Ruetschi defect, form easily on NiO surfaces and play a significant role in O-vacancy formation. , Accordingly, considerable efforts have been made to promote O-vacancy formation by regulating Ni vacancies in NiO catalysts via tuning the crystal structures, morphologies, and exposed crystal facets. ,,− Among these, crystal facet engineering has been highlighted as a promising strategy because different crystal facets of NiO have their own atomic arrangement patterns and thus distinctive electronic structure, which is believed to result in differences in Ni vacancies and thus dramatically influence O-vacancy formation. For example, Tian’s group has found that cubic NiO with (100) facets possessed abundant Ni vacancies and thus promoted O-vacancy formation, which resulted in more ROS formation and thus facilitated CTO.…”

Promoting the Catalytic Ozonation of Toluene by Introducing SO42– into the α-MnO2/ZSM-5 Catalyst to Tune Both Oxygen Vacancies and Acid Sites

“…Noble metals and transition metal oxides, including Pt, Ag, Cu, Mn, Ce, Ni, etc., ,− were widely investigated as highly efficient catalysts for catalytic ozonation of toluene. Among them, manganese oxides with various crystalline phase, such as α-, β-, γ-, and ε-types, have received enormous attention by virtue of their superior capability for converting ozone into active oxygen species at ambient temperature and lower price compared to noble metals. − However, toluene conversion on Mn-based catalysts generally decreased significantly under humid conditions, and one of the reasons is the deactivation caused by the competitive adsorption of water on the catalyst surface. − Doping Mn oxides into ZSM-5 is a promising strategy to overcome the bottleneck because ZSM-5 with a proper Si/Al molar ratio possesses excellent hydrophobicity, which effectively prevents the active sites for catalytic ozonation of toluene from being covered by water molecules. ,− Nevertheless, as reported by Huang’s and Kim’s groups, , although MnO x has achieved excellent toluene conversion by adopting ZSM-5 as a support to alter the surface hydrophobic ability, the ozonation efficiency, CO x selectivity, and so on remains unsatisfactory and needs further improvement .…”