Summary Solid sorbents adsorption is considered as one of the potential options for CO2 capture process. The success of this approach is dependent on the development of an adsorbent with a high CO2 adsorption capacity, in a broad temperature window. In this study, we have investigated the CO2 adsorption on highly ordered three dimensional mesoporous MCM-68 (Si/Al ratio 22) as a sorbent material. The interesting features such as high surface area, high thermal stability with ordered mesoporous structure of MCM-68 were found to be advantageous for the CO2 adsorption in broad temperature window.

The mixing conditions have a direct impact on the pore structure of alumina extrudates. We study the pore structure of samples prepared with two mixers: a standard Eirich mixer and a smaller yet more severe Fukae mixer, which operates at 1500 rpm. We present the development of a bimodal pore size distribution within the range of 25-150 angstrom produced by using the Fukae mixer. The pore structure consists of larger pores that grow at the expense of the smaller ones and can be tuned as a function of mixing time.

The adsorption of HNCO on Fe-ZSM5 was investigated in detail by DRIFT spectroscopy and compared to the adsorption on H-ZSM5, Al 2 O 3 , SiO 2 , Fe 2 O 3 /Al 2 O 3 and Fe 2 O 3 /SiO 2 . At 150 °C, HNCO adsorbs dissociatively on Fe-ZSM5 producing principally isocyanate species (–NCO) adsorbed on Al and Fe sites. In the presence of water the hydrolysis of the –NCO groups to NH 3 was observed. Comparison of the DRIFT results with measurements of the catalytic activity of coated cordierite monoliths suggests that –NCO groups are likely intermediate species in the hydrolysis of HNCO over Fe-ZSM5.

Fe-ZSM5 was prepared with high iron content by solid-state ion exchange and characterized by ICP-AES, BET surface measurements, TEM, UV–vis, EPR and DRIFT spectroscopy as well as supplementing catalytic tests in order to clear up its functionality in urea-SCR. Due to the over-exchange with iron small Fe2O3 particles were formed, identified by UV–vis, EPR and TEM measurements, which were proved to be not active for the SCR reaction. However, the oxidation of NO to NO2 over Fe3+ ions in the catalyst was realized to be a pre-requisite for the SCR reaction and the rate-determining step. DRIFT investigations under SCR conditions showed adsorbates on Fe2+ up to 300°C. The high SCR activity above 300°C can be explained by the faster reoxidation of Fe2+ to Fe3+ sites at high temperatures. The observed inhibition of the SCR reaction by excess ammonia at low and intermediate temperatures can be explained in this context by the reducing properties of ammonia converting Fe3+ to Fe2+ or by preventing the reoxidation of Fe2+.

The influence of NO2 on the selective catalytic reduction (SCR) of NO with ammonia was studied over Fe-ZSM5 coated on cordierite monolith. NO2 in the feed drastically enhanced the NOx removal efficiency (DeNOx) up to 600°C, whereas the promoting effect was most pronounced at the low temperature end. The maximum activity was found for NO2/NOx=50%, which is explained by the stoichiometry of the actual SCR reaction over Fe-ZSM5, requiring a NH3:NO:NO2 ratio of 2:1:1. In this context, it is a special feature of Fe-ZSM5 to keep this activity level almost up to NO2/NOx=100%. The addition of NO2 to the feed gas was always accompanied by the production of N2O at lower and intermediate temperatures. The absence of N2O at the high temperature end is explained by the N2O decomposition and N2O-SCR reaction. Water and oxygen influence the SCR reaction indirectly. Oxygen enhances the oxidation of NO to NO2 and water suppresses the oxidation of NO to NO2, which is an essential preceding step of the actual SCR reaction for NO2/NOx<50%. DRIFT spectra of the catalyst under different pre-treatment and operating conditions suggest a common intermediate, from which the main product N2 is formed with NO and the side-product N2O by reaction with gas phase NO2.

Two different iron exchanged zeolites were studied for the hydrolysis of isocyanic acid (HNCO) to ammonia, which is an important intermediate step in the selective catalytic reduction (SCR) of NO with urea. The hydrolysis reaction proceeded with very high activity and selectivity on over-exchanged as well as low-exchanged Fe-ZSM5 catalyst samples. The hydrolysis activity of the catalysts was inversely correlated with their Brønsted acidity, which decreased with the degree of iron exchange and the degree of ageing. Thus, over-exchanged Fe-ZSM5 had the highest activity, which even increased when the catalyst was aged.

Fe-ZSM5 coated on cordierite monolith was investigated in the selective catalytic reduction (SCR) of NO with ammonia over a broad temperature range, applying simulated diesel exhaust gas conditions. The catalyst exhibited over 80% NOx reduction (DeNOx) from 400 to 650°C at very good selectivity. The dosage of variable amounts of ammonia in the catalytic tests revealed that the SCR reaction is inhibited by ammonia. At very high temperatures DeNOx is reduced due to the selective catalytic oxidation (SCO) of ammonia to nitrogen and the oxidation to NO. Water-free experiments resulted in generally higher DeNOx values, which are explained by the inhibiting effect of water on the NO oxidation capability of Fe-ZSM5. The catalyst was stable upon thermal ageing and only 5–15% loss in DeNOx activity was observed after hydrothermal treatment. This loss in DeNOx is in parallel with a loss of ammonia storage capacity of the aged catalyst. Characterization by NH3 TPD and MAS 27Al NMR spectroscopy revealed dealumination of the zeolite by hydrothermal ageing, which reduces the Brønsted acidity of the catalyst.

Thermally stable mesoporous tetragonal zirconia with high surface area (153m2/g at 700°C) has been prepared by using bifunctional ethylene diamine as both precipitating agent for ZrOCl2 to ZrO(OH)2 and colloidal protecting agent for the ZrO(OH)2 nanoparticles. The zirconia sample was found to possess the tetragonal crystal phase exclusively. This approach avoids traditional bases such as NH3, NaOH and expensive surfactants and copolymers, which are usually employed as templates for the synthesis of high surface area and thermally stable metal oxides. Pt nanoclusters of size ∼20–30Å have been prepared in a single step chemical reduction method in aqueous media. The Pt nanoclusters have been deposited on mesoporous (pore size≈35–45Å) hydrous zirconia by adopting the ‘precursor’ route. The Pt nanoclusters have been found almost evenly dispersed in the hydrous zirconia matrix without aggregation. The ethylene diamine likely serves as a link between the support (ZrO(OH)2) and Pt nanoclusters. The Pt/ZrO2 catalyst has been found to be highly active for 1-hexene hydrogenation reactions with a turnover frequency of about 20,000h−1. All systems have been characterized by TEM, EDX, SEM, X-ray diffraction, N2 adsorption–desorption isotherms and TGA.

Fe-ZSM5 coated on a cordierite monolith was characterized and tested in the selective reduction of nitrogen oxides (NOx) with ammonia. More than 70 % of the NOxwere converted at T>350 °C if only NO was present in the feed. For equimolar amounts of NO and NO2in the feed, NOxconversions of over 90 % were reached for T = 200-450 °C. Hydrothermal ageing of Fe-ZSM5 resulted in a small loss in NOxconversion and enhanced N2O formation.