Biomass-Waste-Derived Silica for Solvent-Lean Cu-SSZ-13 Porous Catalysts in NH3-SCR NOx Remediation

The development of biomass-waste-derived functional porous materials can support resource-conscious strategies for environmental remediation. In this study, Cu-SSZ-13 porous catalysts were prepared from rice husk ash as a biomass-derived silica source and metakaolin as the aluminosilicate precursor using solvent-lean vapor-assisted crystallization under OSDA-free or reduced-OSDA conditions. The S1–S8 catalyst matrix was prepared at nominal Si/Al ratios of 12 and 25, with crystallization conducted in the absence or presence of Cu, followed by a common post-synthetic Cu ion-exchange procedure. XRD showed predominant CHA formation across the matrix, while 27Al and 29Si MAS NMR confirmed predominantly tetrahedral Al environments and systematic differences in the silicate-framework response. Final Cu contents ranged from 1.50 to 2.61 wt%, with Cu/Al ratios of 0.22–0.27, and samples crystallized in the presence of Cu showed a consistent tendency toward slightly higher final Cu contents than their paired Cu-free-crystallization counterparts. The fresh catalysts exhibited substantial NH3-SCR activity, with apparent T50 values of 201.3–278.4 °C and maximum NOx conversions of 89.9–97.0%; S4 showed the earliest light-off. Accelerated hydrothermal aging shifted T50 by 32.4–65.3 °C while retaining 91.1–94.9% of the fresh maximum NOx-conversion response. Estimated N2 selectivity remained high throughout most of the principal activity region, whereas relative N2O formation remained limited and increased mainly at elevated temperature. Overall, the results demonstrate that a rice-husk-ash/metakaolin precursor platform can be converted into functional CHA-type Cu-SSZ-13 porous catalysts for NOx remediation using OSDA-free or reduced-OSDA, solvent-lean synthesis while retaining substantial catalytic functionality after accelerated hydrothermal exposure.