Carlos Knapp

Alumina- and titania-based monolithic catalysts for low temperature selective catalytic reduction of nitrogen oxides

Abstract The selective catalytic reduction of NO+NO2 (NOx) at low temperature (180–230°C) with ammonia has been investigated with copper-nickel and vanadium oxides supported on titania and alumina monoliths. The influence of the operating temperature, as well as NH3/NOx and NO/NO2 inlet ratios has been studied. High NOx conversions were obtained at operating conditions similar to those used in industrial scale units with all the catalysts. Reaction temperature, ammonia and nitrogen dioxide inlet concentration increased the N2O formation with the copper-nickel catalysts, while no increase was observed with the vanadium catalysts. The vanadium-titania catalyst exhibited the highest DeNOx activity, with no detectable ammonia slip and a low N2O formation when NH3/NOx inlet ratio was kept below 0.8. TPR results of this catalyst with NO/NH3/O2, NO2/NH3/O2 and NO/NO2/NH3/O2 feed mixtures indicated that the presence of NO2 as the only nitrogen oxide increases the quantity of adsorbed species, which seem to be responsible for N2O formation. When NO was also present, N2O formation was not observed.

Titania based platinum monolithic catalysts for lean-burn DeNOx process

Monolithic catalyst supports were prepared with mixtures of titanium dioxide and a natural magnesium silicate. Some properties of relevance to their scale-up for industrial applications using monoliths manufactured with various commercial titanias and treated at different temperatures were compared. Thus, their textural properties, anatase phase stability and axial strength were evaluated. Taking into account these results, a support was selected for the preparation of platinum catalysts, which were prepared by varying the impregnation time and the platinum solution concentration. Equations were obtained describing the dependence of the catalyst platinum content on each of these parameters. Catalyst activities were tested in the catalytic reduction of nitrogen oxide with propylene in lean-burn conditions.

Phase distribution in titania-sepiolite catalyst supports prepared by different methods

In this study it has been shown that in samples prepared by mechanical mixing of titania and sepiolite, greater titania coverages could be obtained when the mixtures were kneaded in a concentrated acid medium. The distribution of sepiolite and titania at the surface of the mechanical mixtures was studied by the electrophoretic migration technique. The samples were further characterised by nitrogen adsorption, XRD and thermogravimetric techniques. The electrophoretic migration results showed that the addition of sepiolite to titania, kneaded in water, had a dramatic effect on the quantity of titanium oxide present at the support’s surface, both strongly decreasing the molar fraction of titania at the surface, and altering the electrophoretic properties of the mixtures. When kneaded in concentrated acid (HCl, 37%, m/m), the effect of sepiolite addition was greatly reduced. The XRD patterns and BET surface areas of the water-kneaded samples agreed with previously reported results. However, kneading in acid medium induced a slight increase in the BET surface areas of sepiolite and mixtures, but a small decrease for titania. This acid treatment did not alter the XRD patterns of titania and mixtures, compared to the water-kneaded samples. Although the XRD pattern of sepiolite was partially altered, a large part (71%) of sepiolite remained unchanged.

Lean NOx reduction in real diesel exhaust with copper and platinum titania based monolithic catalysts

A study on the catalytic behaviour of a copper and a platinum titania based monolithic catalyst in the reduction of nitrogen oxides with hydrocarbons in real diesel conditions was carried out. A Volvo TD 7.31 engine was used as gas source, and diesel fuel was the reductant. In these conditions, both catalysts were active in the reduction reaction. The influence of various operating parameters on the catalytic activity, as engine speed and reductant concentration in the gas has studied. Other aspects were also studied as selectivity of reduction to nitrous oxide, nitrogen monoxide oxidation into nitrogen dioxide, and generation of carbon monoxide. The selectivity in the reduction of NO to N2O with the diesel exhaust was relatively low with both titania supported systems. Opposite behaviours of both catalysts in NO to NO2 oxidation were observed, indicating two different mechanisms for this reaction

Method for selective removal of supported platinum particles from external zeolite surfaces: characterisation of and application to a catalyst for the selective reduction of nitrogen oxide by hydrocarbons

Abstract A method for selectively removing Pt particles supported on H–ZSM-5 (Pt/H–ZSM-5) from the external surfaces of zeolite crystals was investigated, using a reagent system composed of halogen–tetraethylammonium halide–organic solvent. The influence of the nature of the halogen and the treatment time on the quantity of Pt removed was studied. After treatment of the Pt/H–ZSM-5, the characterisation by hydrogen chemisorption, XPS and TEM indicated that the method is suitable for preparing a zeolite material that contains exclusively Pt particles confined in the grain boundaries of zeolite crystals (enveloped Pt). As an example of its application, the catalytic activity for the reduction of nitrogen oxides (NO x ) with n -dodecane in the presence of oxygen was studied. The results indicate a beneficial effect of removing Pt from the outermost surface of Pt/H–ZSM-5, with an increase in the selectivity of NO x reduction to N 2 from 25 to 45% at the maximum of NO x conversion. This effect was mainly attributed to the hindered access of the bulky hydrocarbon molecules to the enveloped Pt, thus favouring the reaction of the hydrocarbon with NO 2 formed by the oxidation of NO on the Pt sites.

Lean-DeNO(x) titania based monolithic catalysts

The activity of titania based copper and platinum monolithic catalysts in the reduction of nitrogen oxides was studied with exhaust gases from a Diesel engine injecting fuel as reductant. Combining both catalysts, a two-stage system was designed, studying the influence of the copper catalysts composition on its performance with synthetic gas mixtures. The influence of reactants concentration and operating conditions was also investigated. Taking into account these results, a double-bed system with a cell density of 33 cell cm(-2) (210 c.p.s.i.) was prepared. Linear velocity had a strong influence on the performance of the Pt catalyst and of the double-bed. Two NOx conversion maxima were observed with Pt/TiO2 at 225 degrees C and 350 degrees C operating at 6.6 m s(-1). Promising NOx conversions were achieved in the temperature range 200-450 degrees C

Platinum-titania-sepiolite monolithic catalysts for the reduction of nitric oxide with propene in lean-burn conditions

In this work the influence of the support preparation variables on the activity of Pt-titania-sepiolite monolithic catalysts for the reduction of nitrogen oxides with propene in lean-burn conditions was studied. The influence of raw materials were studied using five types of titania. The catalysts activities showed significant differences in the NO X conversions, which were related to the textural properties of the catalysts. Heat treating the support at 800°C induced a fall in the catalysts activity compared to that treated at 500°C. XRD and TG-DSC measurements indicated that this decrease was not due to phase changes either of the titania, or of the sepiolite. MIP and nitrogen adsorption/desorption results indicated that it was due to a large decrease of the surface area. EPMA-WDS line profiles of Pt, Ti, Mg and Si across a monolith wall section indicated that platinum is selectively deposited on titania and homogeneously dispersed within the wall. The influence of area velocity and steam on the activity were also studied.

Low temperature monolithic SCR catalysts for tail gas treatment in nitric acid plants

The performance of new monolithic catalysts for low temperature Selective Catalytic Reduction of nitrogen oxides from nitric acid plants has been studied. Low temperature and low pressure drop offer a lower cost solution for NO x emission control. The porous structure of the catalyst has been improved, thus increasing its effectiveness factor by 5%. This new catalyst concept allows to achieve NO x conversions of about 90 %, with very low NH 3 emissions at 180°C and GSHV of 5900 h -1 (NTP) with a pressure drop of only 1 cm H2O m -1 .