Catalytic Sorbent Research Articles

Low cost catalytic sorbents for NO x reduction. 3. NO reduction tests using NH 3 as reducing agent

Chars and activated chars obtained from a low-rank coal and doped with vanadium compounds (V 2O 5 and NH 4VO 3) and petroleum coke ash, PCA, (Main metal components: V, Fe and Ni) have been tested as catalytic sorbents for NO reduction. The reduction tests have been carried out in the presence of oxygen with the addition of ammonia as reducing agent. The sorbents prepared have shown to be active for NO reduction at low-temperature (150 °C). Higher reduction efficiencies than with the unloaded not activated char have been achieved. The sorbents most efficient are those prepared with activated chars. Doping with vanadium compounds significantly upgrades the behaviour of the activated char. For the samples prepared with PCA, slightly lower NO conversions are observed but it has been shown that PCA is perspective for producing transition metals doped activated carbons. Surface Chemistry affects the sample behaviour. In general terms, the reduction efficiency is promoted by a low acidic character of the surface. However, it cannot be stated that the highest efficiency corresponds to the samples with the lowest CO 2/CO ratio. It reveals that the overall behaviour of the samples responds to a combined effect of the chemical surface of the carbon support and the catalytic activity of the vanadia loaded. The results obtained show that the pathway of reduction when ammonia is used corresponds to a catalytic heterogeneous reaction, in contrast to the uncatalized high temperature (350 °C) reduction observed when ammonia was not used as reducing agent.

Low cost catalytic sorbents for NO x reduction. 2. Tests with no reduction reactives ☆

Coal, char and activated char doped with model vanadium compounds (V 2O 5 and NH 4VO 3) and petroleum coke ash, PCA, (main metal components: V, Fe and Ni) have been tested as catalytic sorbents for NO reduction without the addition of a reduction reactive. The sorbents prepared have shown to be active for NO reduction at temperatures higher than 350 °C. The most efficient sorbents are those obtained from unactivated chars and doping with model vanadium compounds or PCA does not upgrade significantly their behaviour. On the other hand, for the samples prepared from activated char, an improvement of the reduction efficiency is observed after impregnation with model vanadium compounds or PCA. SSA of the samples does not play a relevant role on the NO reduction efficiency while surface chemistry significantly affect the samples’ behaviour: higher the CO 2/CO ratio determined by TPD, higher the NO reduction efficiency of the sample. Slightly higher NO conversions are observed for the samples loaded with pure compounds but PCA is perspective for producing catalyst doped activated carbons.

Low cost catalytic sorbents for NO x reduction. 1. Preparation and characterization of coal char impregnated with model vanadium components and petroleum coke ash

Spanish coal, char and activated char doped with model vanadium components (V 2O 5 and NH 4VO 3) and petroleum coke ash (enriched in V, Fe, and Ni) were prepared and characterized as potential catalytic sorbents for NO x reduction. The phase-mineral and chemical composition, content and behavior (capture, retention, distribution, and redistribution) of transition metals, as well as morphogenesis, surface area, acid–base properties, surface active sites and oxidation–reduction transformations of the catalytic sorbents were characterized. It was found that minerals and phases such as anhydrite, calcite, clay minerals, pyrite, pyrrhotite, magnetite and fusinoid-type ingredients have a leading role for the behavior of loaded transition metals. Some original (pyrite, jarosite, shcherbinaite, coulsonite, trevorite, Ni oxide) and newly formed (pyrrhotite, magnetite, wuestite, hematite, paramontroseite, karelianite) Fe, V and Ni minerals in the catalytic sorbents are perspective redox indicators for the physicochemical conditions in such complex system. The data indicate that the V–Fe–Ni containing minerals dispersed onto and into the carbon support may be the most active catalytic sites. The preparation procedure that could provide the most favorable conditions for the production of effective and low cost catalytic sorbents for NO x reduction is also described.