Study on the effect of ZrO2 loading on the formation of CuO-ZnO-ZrO2-Al2O3/ZrO2-modified HZSM-5 bifunctional catalysts as potential catalysts for CO2 valorization

Carbon utilization technologies have gained increasing attention as an effective strategy for mitigating atmospheric CO₂ emissions through conversion into value-added products such as methanol and dimethyl ether (DME). In recent studies, bifunctional catalysts integrating metallic and acidic functions have emerged as a promising approach to overcome challenges associated with direct DME synthesis from CO₂. However, studies on bifunctional catalysts particularly with respect to structural integration and acid–base tuning remain limited. In this work, bifunctional CuO-ZnO-ZrO 2 -Al 2 O 3 /xZrO₂-modified HZSM-5 catalysts (x = 0–10 wt%) were synthesized and characterized using FESEM, XRD, EDX, FTIR, TGA, BET, and NH₃-TPD analyses. Morphological and XRD analyses confirmed the successful integration of ZrO₂-modified HZSM-5 with CuO-ZnO-ZrO 2 -Al 2 O 3 , while elemental mapping showed uniform dispersion of Cu, Zn, Zr, Si, and Al in the catalyst. TGA results showed that intermediate ZrO₂ loadings (up to 7.5 wt%) exhibited lower weight loss, suggesting a potential enhancement in thermal stability. BET analysis showed that low ZrO₂ loading (2.5 wt%) reduced the specific surface area whereas higher loadings (up to 10 wt%) increased surface area, which may be associated with deposition of impregnated ZrO 2 on the external surface of the catalyst. In addition, increasing ZrO₂ loading led to a reduction in average pore diameter. Changes in pore volume were also observed with increasing ZrO 2 loading, indicating that the impregnated ZrO 2 influenced the pore structure of the catalysts. NH₃-TPD analysis demonstrated that ZrO₂ incorporation significantly modified the acid-site distribution by suppressing strong acid sites and promoting weak-to-moderate acidity. At 10 wt% ZrO 2 loading, an increase in total acidity was observed, which may be associated with the contribution of acid sites from the impregnated ZrO₂. Overall, ZrO₂ loading plays a critical role in tuning the structural, textural, acidic, and thermal properties of the bifunctional catalyst, providing important insights into the rational design of integrated catalysts for future CO 2 valorization applications.