Precious metal-based Catalytic Membrane Reactors for continuous flow catalytic hydrodechlorination.

This work is focused on the development of Catalytic Membrane Reactors (CMRs) comprising precious metals as active phases for a comparative assessment in continuous-flow catalytic hydrodechlorination (HDC). HDC has proved its remarkable potential for application as polishing step in drinking water treatment plants, but studies operating in continuous mode are scarce. Preliminary experiments were conducted in batch operation using Pd/Al 2 O 3 , Rh/Al 2 O 3 and Pt/Al 2 O 3 powder catalysts to evaluate the influence of the active phase on the removal of prochloraz (PCZ) (100 μg L⁻¹), a pesticide listed on the EU Watch List (2022 /1307), by HDC. PCZ removal was successfully described by a pseudo-first order kinetic equation and reaction pathways were proposed. Among the catalysts tested, Pt-based suffered a significant deactivation, not warranting the elimination of this micropollutant. Pd/Al 2 O 3 exhibited a faster removal of PCZ than Rh/Al 2 O 3 , while this catalyst resulted in further hydrogenation of the non-chlorinated reaction product. Accordingly, different CMRs were developed by decorating cylindrical inert porous alumina membranes with Pd, Rh, and a combination of Pd-Rh as active phases (∼1% wt.). All CMRs showed a remarkable stability along 100 h on stream, being Pd/CMR be the most effective, with a pseudo-first order rate constant value of 0.062 min⁻¹. An assessment of the impact of operating conditions (aqueous flow rate, PCZ initial concentration, temperature and H 2 flow rate) was conducted using the Pd/CMR, which notably remained stable for 450 h on stream. The versatility of the system was finally demonstrated in tap water, achieving a steady-state PCZ conversion close to 95 %. [Display omitted] • HDC is effective for the removal of PCZ using Pd/Al 2 O 3 and Rh/Al 2 O 3 catalysts. • PCZ removal rate was accurately described by a pseudo-first order kinetic equation. • Sequential reaction pathways were proposed depending on the catalytic active phase. • CMRs were highly active and stable, showing the Pd/CMR an outstanding performance. • Pd/CMR feasibility was proved at varying operating conditions, even in tap water. [ABSTRACT FROM AUTHOR]