The activation of NO and CH4 for NO-SCR reaction over In- and Co-containing H-ZSM-5 catalysts

Amino-acid modulated hierarchical In/H-Beta zeolites for selective catalytic reduction of NO with CH4 in the presence of H2O and SO2

Selective catalytic reduction of NO with CH₄ (CH₄-SCR) has been studied over a series of amino-acid mediated hierarchical beta zeolites with indium exchange. Amino acid mesoporogens greatly affect the NO reduction (DeNO_x) efficiency of In/H-Beta catalysts. Mesoporous In/H-Beta-P synthesized using proline exhibits the highest NO_x removal efficiency of 40% in excess oxygen and poisonous SO₂ and H₂O, 10% higher than our previously optimized In/H-Beta catalyst using commercial beta zeolites with a similar Si/Al ratio. Analyses using XRD, N₂ adsorption-desorption, EPR, SEM, TEM, EDX, ICP, ²⁷Al and ²⁹Si MAS NMR, XPS, H₂-TPR, NH₃-TPD, and Py-IR reveal that amino acids promote beta crystallization, modulate zeolite acid sites and surface oxygen species, and generate hierarchical pore architectures without affecting the Si/Al ratio, indium content, and percentage of the active InO⁺ species. The mosaic-structured In/H-Beta-P exhibits the strongest Brønsted acidity and surface labile oxygen which enhance the oxyindium interaction with the zeolite framework, promoting CH₄-SCR activity. The strong acidity, surface active oxygen species, and mesopores lead to excellent stability of the In/H-Beta-P catalyst in the presence of SO₂ and H₂O, withstanding several catalytic DeNO_x cycles under harsh reaction conditions.

Mechanism of Propane Adsorption and the Following NO x Reduction over an In/BEA Catalyst: A Computational Study

To expand the knowledge on hydrocarbon selective catalytic reduction (SCR) and follow the research steps of methane-SCR and propane-SCR in our previous work, we studied the characteristics of propane adsorption on In/BEA zeolite, explored the NO and NO₂ activation process on a propane adsorbed catalyst, and calculated the reaction enthalpy of two reaction pathways. Results showed that O site in the L-model (the [InO]⁺/BEA structure) was the main active site in the adsorption process, and any of the carbon atoms in the propane molecule could react with it, with a lower adsorption energy than methane (-3.20 vs -2.98 eV). Also, NO or NO₂ could not be directly activated on the propane adsorbed catalyst, indicating that the process may be complicated. In addition, propane reduces the NO or NO₂ molecule with two different pathways and the final products were less stable than those of methane (-5.6 vs -20 eV). These results could explain the fact that propane and methane had different reaction temperatures and would further deepen our understanding of the propane-SCR process.

Mechanism of the selective catalytic reduction of NOx with CH4 on In/H-beta

Firstly, CH₄ would be activated to CH₃OH, subsequently, CH₃OH and O* reacted to generate HCOO⁻. Finally, the HCOO⁻ further reacted with NO₃⁻ which was completely converted to CO₂, H₂O and N₂.

Identification of Main Active Sites and the Role of NO2 on NOx Reduction with CH4 over In/BEA Catalyst: A Computational Study

The main active sites and the catalytic process in selective catalytic reduction of NOx by CH4 (CH4-SCR) on In/BEA catalyst were investigated by density functional theory (DFT) using a periodic model. The [InO]+ and [InOH]2+ moieties were constructed in the channel of periodic BEA zeolite representing the Lewis and Brønsted acid sites. The electronic structures [InO]+ and [InOH]2+ were analyzed, and it was found that the [InO]+ group were the main active sites for CH4 activation and NO/NO2 adsorption in the CH4-SCR process. CH4 molecules could be activated on the O site of the [InO]+ group in In/BEA, which was resulted from the strong interactions between the C-p orbital of the CH4 molecule and the O-p orbital of the [InO]+ group. CH4 activation was the initial step in CH4-SCR on In/BEA catalyst. NO2 molecules were essential in the SCR process, and they could be produced by NO reacting with gaseous O2 or the O atom of the [InO]+ group. The presence of NO2 could facilitate the key intermediate nitromethane (CH3NO2) formation and lower the reaction barrier in the SCR process.

NO-CH4-SCR Over Core-Shell MnH-Zeolite Composites

Selective catalytic reduction of NO with methane (NO-CH4-SCR) in the presence of excess oxygen was investigated over the synthesized MnH-ZZs-n zeolite composite catalysts with FAU (as core) and BEA (as shell) topologies. XRD, SEM, and NH3-TPD technologies were employed to characterize the catalysts. It is found that the topological structure of the zeolite affected the catalytic properties and H2O/SO2 tolerances considerably. MnH-ZZs-n catalysts exhibited much higher NO-CH4-SCR activity than the physical mixture catalysts with comparable relative mass content of Y and Beta zeolites, particularly the ratio of Y and Beta at the range of 0.2–0.5 than the MnH-Beta catalysts with single topology. NH3-TPD results showed that one new type of strong acidic sites formed in H-ZZs-n and remained in MnH-ZZs-n resulted from the interaction between the Lewis and Brönsted acid sites under a particular environment. The special zeolite-zeolite structure with ion-exchanged Mn ions in the core-shell zeolite composite catalysts contributed to the novel NO-CH4-SCR properties.

The Cooperative Effect of In2O2and In/HZSM-5 for Reduction of Nitric Oxide with Methane

Compared with In/HZSM-5 catalyst, In/HZSM-5/In2O3catalyst that contained two different kinds of In induced by the impregnation and the physical mixing method, respectively, has shown remarkable activity for methane selectively catalytic reduction (CH4-SCR) of NOx. The addition of In2O3to In/HZSM-5 could improve the NO conversion. When a little In2O3was added to the In/HZSM-5, the active sites of InO+which can adsorb NO2were increased. Moreover, at the internal surface of HZSM-5, highly dispersed In2O3species could promote oxidation of NO to NO2. The adsorption of NO2is the key step for the whole reaction, which benefits the activation of methane and the reduction of NOxby methane. Thus the activity of In/HZSM-5/In2O3for CH4-SCR of NOxwas higher than that of In/HZSM-5.