María José Illán-Gómez

Potassium-containing briquetted coal for the reduction of NO

Abstract The reduction of NO by potassium-containing activated carbons and briquettes prepared from a bituminous coal was investigated. Partial washing of KOH activated carbons produced samples with different potassium contents. Briquetting with a binder containing potassium, at different binder/coal ratios, also allowed carbons with different potassium contents to be obtained. The NO-carbon reaction was studied with a fixed-bed flow reactor at atmospheric pressure in two types of experiment: (1) isothermal reaction at 300–600°C; (2) temperature-programmed reaction (TPR) in an NO-He mixture. The reaction products were monitored in both cases, allowing detailed oxygen and nitrogen balances to be determined. Both the potassium remaining in the activated carbons and that present in the briquettes act as a catalyst for the NO-carbon reaction. Therefore, the briquettes are active for NO reduction with the advantage of being produced by a much simpler process with no KOH consumption and no washing process. Furthermore, the briquettes can be moulded in the desired form with appreciable mechanical strength. The final potassium loading controls the capacity of the potassium-carbon samples for NO reduction. The reduction of NO by the potassium-containing briquettes is enhanced by the presence of oxygen.

Thermal treatment effect on NO reduction by potassium-containing coal-briquettes and coal-chars

This communication reports the NO reduction activity of potassium containing coal-briquettes prepared at different pyrolysis temperatures. For comparative purposes coal-chars prepared at the same temperatures have also been analyzed. NO reduction experiments were performed in a fix-bed flow reactor at atmospheric pressure using two types of experiment: (i) temperature programmed reaction in a NO/He mixture; and (ii) isothermal reactions at 600°C. The reaction products were monitored in both cases, thus allowing detailed oxygen and nitrogen balances to be determined. It has to be pointed out that a previous in situ heat treatment in He before reaction is necessary for the low temperature activity of potassium containing coal-briquettes. For fresh briquettes, NO direct attack in addition to NO conversion by the catalytic action of potassium is observed at high temperatures. The NO direct attack, both in potassium containing samples and coal-chars, is clearly manifested by a nitrogen imbalance.

Effect of the Support in de-NOx HC-SCR Over Transition Metal Catalysts

Several catalysts based on transition metals (Cu, Co, Fe) and different supports (ZSM-5, activated carbon, Al2O3) have been tested by Temperature-Programmed Reaction (TPR) experiments for the selective catalytic reduction of NOx with propene in the presence of excess oxygen, simulating lean-burn conditions. The activity order with respect to the metal was Cu∼Fe>Co for all supports used. ZSM-5 catalysts have a superior behavior over Al2O3, as observed for noble metal catalysts. Application of activated carbon as a support is not practical due to its consumption at the reaction temperatures. The selectivity to N2 of the catalysts was also independent of the support, being higher than 95% in all the cases.

Reduction of NO by Propene Over Pt, Pd and Rh-Based ZSM-5 Under Lean-Burn Conditions

Selective catalytic reduction of NO by propene has been investigated over noble metal (Pt, Pd, Rh)-based ZSM-5 catalysts. These samples were tested in a gas mixture system in the presence of excess oxygen, simulating lean-burn exhaust gases. The sequence in activity for NO reduction was Pt > Rh ∼ Pd. Regarding the selectivity of the reaction to N2, an opposite trend was observed: Rh > Pd ∼ Pt. The catalytic systems have presented stable operation under isothermal conditions during time-on-stream experiments.