Lars A.H. Andersson

Characterisation of Silica-Titania Mixed Oxides

Abstract A series of coprecipitated silica-titanias containing between 0 and I00 mol% titania were characterized by various methods. These materials are often used as supports for catalysts in the reduction of NO x and are shown to be micro-, meso-, and macroporous. All textural quantities decrease with the addition of TiO 2 to SiO 2 . The macroporosity, of vital importance in the highly diffusion-controlled NO x reduction, reaches a maximum value at 50 mol% TiO 2 . X-ray diffraction, FT-IR, and XPS studies showed that the materials, calcined at 723 K, consisted of a SiO 2 -TiO 2 glass phase, an amorphous silica phase, and an anatase phase. At I0 mol% TiO 2 , rutile was observed, by XRD, in addition to anatase. XPS data indicate the presence of a TiO 2 phase in all Ti-containing samples, a SiO 2 phase at and below 50 mol% TiO 2 , and a SiO 2 -TiO 2 phase at and above 75 mol% TiO 2 . The quantitative XPS analysis indicates a heterogeneous distribution of phases with an increased surface concentration of Si phases. Similar results were obtained by the FT-IR studies, which additionally indicate the presence of surface free silanol groups in all samples and detect tetrahedrally substituted Ti 4+ in the SiO 2 phase.

Catalytic Reduction of Nitrogen Oxides on Mordenites: Some Aspects on the Mechanism

Abstract The emission of nitrogen oxides is a global environmental problem. The ultimate solution would be a catalytic decomposition of NO to N2 and O2. Presently no success has been achieved in developing a suitable catalyst. A working technology to eliminate nitrogen oxides from stationary sources is the Selective Catalytic Reduction (SCR) of nitrogen oxides with ammonia. Since 1983 we have been working with SCR and then initially using V2O5 catalysts. We have found that the reaction rate for equimolar mixtures of NO and NO2 is much higher than that for each gas alone. Since the NOx emissions in flue gases consist of 95% No it is necessary to convert 45% to NO2 to take advantage of the increased activity. The idea was to combine a catalyst for the oxidation of No to NO2 and a catalyst for the reduction step. The chosen catalyst, Nortons Zeolon 900 H, is a good oxidation catalyst for NO and a fairly good reduction catalyst. To enhance the oxidation activity, the zeolite was exchanged with transition metal ions. In contradiction to our expectations the result was a decrease in the activity. However the activity in the reduction of NO to water and nitrogen was greatly enhanced. This is an interesting coupling between the oxidation and the reduction activity, and a link between mordenite and V2O5. V2O5 is also a very good reduction catalyst and a very poor oxidation catalyst for NO. Both the oxidation and reduction activities are depending on the aluminium content in the H-mordenite. The metallic ion is bonded to the zeolite framework on the site where strong Lewis acids are formed on dehydroxylation. The decrease in the oxidation activity is caused by this decreased formation of strong Lewis acids. The ionization of NO-NO2 mixtures to NO+ and NO2− species attached to the surface can explain their catalytic behaviour. In a similar way NO2 alone forms an ion pair with itself. Eventually the same thing applies to mixtures of NO and O2.

Catalytic Reduction of Nitrogen Oxides, 1. The reduction of NO

Abstract The selective catalytic reduction of NO with NH3 has been studied over V205/SiO2-TiO2 catalyst. The influence of side reactions has bee

An infrared and electrical conductance study of V2O5/SIO2-TIO2 catalysts active for the reduction of NO by NH3

Abstract A series of V 2 O 5 SiO 2 TiO 2 catalysts (vanadia content 2–30 wt%) was evaluated for the selective reduction of NO by NH 3 . Activities at 200 °C determined on a per gram vanadia basis were nearly equal for catalysts containing 5–20% vanadia. The 10% catalyst exhibited the highest activity at 350 °C. Characterization of the catalysts with FTIR and XRD showed that the vanadia was highly dispersed on the carrier as an amorphous phase for all catalysts with 20% or less vanadia. Electrical conductance measurements were made to study the dispersion of the vanadia on the support and the effect of different gases on the degree of vanadia reduction. Conductances for the catalysts in 1.5% O 2 Ar carrier gas increased with increasing vanadia content for catalysts with 15% or more vanadia indicating a decreasing distance between V(IV) centers. Exposure of the catalysts to NH 3 in the carrier gas resulted in reversible increases in conductance for all vanadia concentrations. Exposure of the catalysts to NO resulted in reversible conductance increases for the 15, 20, and 30% catalysts. Exposure of the catalysts to NH 3 + NO resulted in conductance changes which indicated a reaction at 350 °C between adsorbed, laterally mobile NH 3 and gaseous NO for all catalysts with the most effective reaction occurring on the 10% catalyst. At 200 °C, the conductance measurements indicated a reaction between strongly bound NH 3 , which exhibited little lateral movement, and gaseous NO.

Selective catalytic reduction of NOx over acid-leached mordenite catalysts

Abstract Selective catalytic reductions of NO, NO 2 and mixtures of NO and NO 2 over mordeninte catalysts were studied. The activity of mordenite catalysts with different Si/Al ratios, obtained through acid leaching, decreased with the Al content of the mordenite. The change activity with temperature and acid leaching together with the changes in contents of Fe and Al indicate that Lewis acids are active sites. These Lewis acids could be either Fe ions or Lewis acids formed on dehydroxylation of Broensted acid sites. Activities of NO reduction on leached mordenites were correlated to the amount of adsorbed NO + measured by IR. The activity in the reduction of NO x revealed a maximal conversion at a NO 2 /NO x ratio of 0.5, indicating that the oxidation of NO or the decomposition of NO 2 are the rate limiting step in the overall reduction.

Catalytic Reduction of Nitrogen Oxides, 2. The reduction of NO2

Abstract The selective catalytic reduction of NO2 with NH3 has been studied over a V2O5/SiO-TiO2 catalyst. The activity for the main reaction was measured between 420 and 670 K. Also reported are activities for the decomposition of NO2 to NO and O2 and the influence of O2 in that reaction. The reaction system NO2-O2-NH3 in N2 has been investigated in detail and activities in single as well as composed reaction media are reported.

Dealuminated mordenites as catalyst in the oxidation and decomposition of nitric oxide and in the decomposition of nitrogen dioxide: characterization and activities

Abstract Dealuminated mordenites were investigated in order to illustrate the effect of the aluminium content on catalytic and physicochemical characteristics. Chemical and physical characterizations of the catalysts were performed by means of X-ray diffraction, chemical analysis, adsorption- and desorption studies and IR-measurements. The catalysts were tested in the oxidation of NO and in the decomposition of NO 2 and NO. Activities for the mordenites in both the oxidation of NO and the decomposition of NO 2 were strongly dependent on the aluminium content of the catalyst. The highest activities were obtained for the original unleached catalyst. No direct decomposition of No to N 2 and O 2 was observed in the temperature range from 420 to 690 K. Adsorbed amounts of No and NH 3 showed a regular decrease with the amount of aluminium in the catalyst. The activities in the oxidation of NO and the decomposition of NO 2 could be correlated to the amount of NO + adsorbed on the catalyst and which was detected by IR.

Fast pyrolysis of sawdust in an entrained flow reactor

Abstract Fast pyrolysis of sawdust was investigated over a temperature range of 1000–1400 °C, a particle residence time of 0.56–1.0 s, and particle size fractions ranging from 250 to 630 μm. A medium-c.v. gas was produced throughout the course of the investigation. For most experiments, material balance calculations showed that more than 87 % of the sawdust fed into the system was accounted for in the product streams. With the exception of the lowest temperature and shortest residence time, the calculated cold gas efficiency was over 70% for all the experiments, with an average of ≈79%. At higher temperatures no tar was observed.

High Temperature Gasification of Biomass in an Atmospheric Entrained Flow Reactor

An entrained flow reactor has been constructed in order to study gasification of biomass at high temperatures (1273-1673 K). High temperatures were chosen while particular interest was found in how to maximize the gas product formation without using a separate tar cracking step. It was further the incentative to investigate the influence of the high temperature on the product formation at short residence times (0.25-0.8 s) in different gas atmospheres (H20/N2CO2/N2).

Investigation of peat pyrolysis under inert gas atmosphere

Seven Swedish peats of different degrees of humification were pyrolysed in a thermobalance at pressures in the range 1.0-4.0 MPa. The formation kinetics of the pyrolysis products were determined using the non-isothermal evaluation method. The sample size used was 1.0 g and the heating rate was 10 K min-1. Gas production was analysed by gas chromatography and the components were CO2, C2H4, C2H6, CH4 and CO. The tar and char production were measured after the experiment by weighing. The experiments showed that gas production was slightly increased, at the expense of tar production, with increasing pressure, indicating some thermal cracking. The kinetic parameters, i.e. pre-exponential factor, k0, and activation energy, E(a), were unaffected by the pressure. (Less)