**4. Conclusions**

Energy production is associated with many environmental risks; e.g., generating greenhouse gas emissions and nitrogen oxides (NOx) are among the primary gas pollution concerns. Environmental catalysis plays a pivotal role in NOx mitigation (DeNOx). This study investigated a collection of ceramic foams as a potential catalyst support for selective catalytic NOx reduction (SCR). To be an attractive support, we should functionalize the surface of raw foams. A library of ceramic SiC, Al2O3, and ZrO2 foams ornamented with nanorod ZnO and TiO2 as W and V oxide coatings was obtained for the first time. We characterized the surface layer structure using XPS, XRF, and SEM and TEM microscopy to optimize the W to V molar ratio.

NOx generation, pollution, and reduction are complex problems. First, combustion in air yields two forms of NOx, namely NO and NO2, in the ratio NO/NOx of 0.90 to 0.95. However, the dominating NOx form in the atmosphere is NO2 resulting from NO oxidation. Accordingly, the main issue in the environmental catalysis of NOx refers to NO, while the main topics of NOx ecotoxicology refer to NO2. Low NO2 content in flue gases also decides NO2. SCR is tested only very rarely, even though a complex NO/NO2 SCR should support a standard NO SCR; therefore, here, we used the NO2 SCR model.

Comparing TiO2 and ZnO systems reveals that the SCR conversion on ZnO appeared superior vs. conversion on TiO2, while the SiC-supported catalysts were less efficient than Al2O3 and ZrO2-supported catalysts. The energy bands in optical spectra correlate with the observed activity rank. However, a more detailed study is needed to assess whether this effect is coincidental only.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/en15051798/s1, Table S1: The amount of metal needed to obtain vanadium, tungsten, or mixed catalysts calculated at 990 mg of the carrier; Table S2: NOx decomposition data for V and W oxides deposited on different carriers. Gas flow rate of 3 [dm3/h]; Table S3: EDXRF analyses of Ti, W, and V nanoparticles deposited on powder or foam Al2O3, SiC, and ZrO2; Table S4: The average crystallite size and lattice parameters of investigated materials determined by XRD method; Figure S1: High-resolution XPS spectra of (a) O1s and V2p, (b) C1s, (c) W4f, and (d) W4d. The red spectra represent 1.0% W,V/ZnO/ZrO2 system, the blue—the 1.0% W,V/ZnO/Al2O3 system, and the green—1.0% W,V/ZnO/SiC system; and Figure S2: UV-Vis spectra of TiO2/SiC or TiO2/Al2O3 and ZnO/SiC or ZnO/Al2O3 in powders.

**Author Contributions:** Conceptualization, M.K. and J.P.; formal analysis, J.P., M.K. and P.B.; writing— original draft preparation, M.K., J.P., T.S., P.B., R.S., M.Z., J.S., K.B., B.S.W., M.O., R.P. and M.G.; writing—review and editing, P.B. and M.K.; visualization, M.K.; supervision, J.P. and T.S.; project administration, J.P. and P.B.; funding acquisition, J.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research study was funded by the National Centre for Research and Development in Poland, gran<sup>t</sup> no. TANGO1/266384/NCBR/2015, and National Science Center, gran<sup>t</sup> no. OPUS 2018/29/B/ST8/02303.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The datasets generated during the current study are available from the corresponding authors upon reasonable request.

**Acknowledgments:** For the support, Jaroslaw Polanski would like to acknowledge Zielony Horyzont: New Energy project ZFIN 40001022.

**Conflicts of Interest:** The authors declare no conflict of interest.
