Nitrate Catalytic Reduction over Bimetallic Catalysts: Catalyst Optimization

• Main Authors: A. Sofia G. G. Santos, João Restivo, Carla A. Orge, M. Fernando R. Pereira, O. Salomé G. P. Soares
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: C
• Subjects: catalytic reduction; nitrate removal; bimetallic catalysts; carbon nanotubes; titanium dioxide
• Online Access: https://www.mdpi.com/2311-5629/6/4/78

The catalytic removal of nitrate (NO₃⁻) in water using hydrogen as a reducing agent was studied using palladium-copper bimetallic catalysts in different supports. Commercial carbon nanotubes (CNTs), used as received and with different mechanical (CNT(BM 2h)) and chemical modifications (CNT (BM 4h)-N), titanium dioxide (TiO₂) and composite materials (TiO₂-CNT) were considered as main supports for the metallic phase. Different metal loadings were studied to synthesize an optimized catalyst with high NO₃⁻ conversion rate and considerable selectivity for N₂ formation. Among all the studied support materials, the milled carbon nanotubes (sample CNT(BM 2h) was the support that showed the most promising results using 1%Pd-1%Cu as metallic phases. The most active catalysts were 2.5%Pd-2.5%Cu and 5%Pd-2.5%Cu supported on CNT(BM 2h), achieving total conversion after a 120 min reaction with N₂ selectivity values of 62% and 60%, respectively. Reutilization experiments allowed us to conclude that these catalysts were stable during several reactions, in terms of NO₃⁻ conversion rate. However, the consecutive reuse of the catalyst leads to major changes concerning NH₄⁺ selectivity values.