The formation of nitrogen oxides (NO_x) during a combustion process is difficult to avoid because of the large exotherm and the consequent problem of avoiding local high-temperature spikes. Consequently, for many applications, such as for automotive power generation, there will be a continuing need to use catalytic after-treatment to reduce harmful emissions. The investigation of the mechanisms of the key catalytic reactions in environmental catalysis can provide an insight into the action of the catalyst, and time-resolved methods offer a powerful means to study these processes under realistic conditions. The use of Temporal Analysis of Products (TAP) and Steady State Isotopic Transient Kinetic Analysis (SSITKA) methods to investigate the reduction of NO_x under various experimental conditions is described. From a detailed analysis of the SSITKA profiles, it is shown that at low temperatures the mechanism for the formation of N₂ and N₂O from NO may differ from the conventional high-temperature mechanism. This is supported by density functional theory calculations, which show that the barrier to the formation of N₂O from the reaction of N(ads) and NO(ads) may be too high to allow this process to occur at low temperatures. The alternative reaction of NO(ads) + NO(ads) = N₂O(g) + O(ads) is shown to be much more favorable and is consistent with the SSITKA analysis. The remarkable effect of hydrogen as a reductant at low temperatures is described, and alternative interpretations of the role of hydrogen are discussed.

In order to study the dehydrogenation of ethylbenzene to styrene, epitaxial iron oxide model catalyst films with Fe₃O₄(111), α-Fe₂O₃(0001) and KFe_xO_y(111) stoichiometry were prepared in single crystal quality on Pt(111). They were investigated using surface science techniques before and after atmospheric pressure reaction experiments in a newly designed single crystal flow reactor. As expected from low-pressure measurements, Fe₃O₄(111) is catalytically inactive. The catalytic activity of α-Fe₂O₃(0001) starts after an activation period of about 45 min. After that, the surface is essentially clean but shows a high concentration of defects. On the potassium-promoted films, however, the activation period is much longer, the activity then is higher and the surface gets covered completely with carbon and oxygen during reaction. This indicates a different reaction pathway on the promoted films with a carbon–oxygen species as catalytically active species.

Silica-supported iron catalysts (Fe/SiO₂, FePt/SiO₂, and FePtK/SiO₂) were prepared using a novel nonaqueous (acetone) evaporative deposition technique. This preparation leads to relatively well-dispersed iron phases at modest (10%) metal loadings. Moreover, catalytic activities of these catalysts for Fischer–Tropsch synthesis are high and comparable to industrially relevant precipitated iron catalysts. Catalyst activities were tested following a nonregular L18 orthogonal array that enabled the number of 150-h activity tests to be reduced from 54 to 18; this statistical design was augmented with five additional runs to provide replication. Primary independent variables affecting catalysts' activity were promoter type, pretreatment gas composition (H₂, H₂/CO, or CO), pretreatment temperature (250, 280, or 320 °C), and reaction temperature (250 or 265 °C); iron carbide level measured from Mössbauer spectroscopy was correlated with activity in a separate analysis. Activity was found to increase in the order Fe/SiO₂, FePt/SiO₂, and FePtK/SiO₂. For a given catalyst composition, activity increases to a maximum with increasing pretreatment temperature and increasing time. Catalyst activity was also positively correlated with increasing chi-carbide content for Fe/SiO₂ and FePt/SiO₂ catalysts but not for FePtK/SiO₂. While pretreatment atmosphere greatly influences initial activity–time behavior, activity is less dependent on pretreatment after about 150 h of reaction. Steady-state methane and C₂₊ hydrocarbon selectivities (CO₂-free basis) for the FePtK/SiO₂ catalyst at 250–265 °C, 10 atm, and H₂/CO = 1 are 7–9 and 91–93%, respectively, while its hydrocarbon productivity at 250 °C (normalized to 15 atm, H₂/CO = 0.7) of 0.27 g HC/g_cat/h is comparable to those reported for unsupported precipitated iron catalysts of high activity and selectivity. These results indicate that preparation of an active, selective, stable, attrition-resistant supported iron catalyst for Fischer–Tropsch synthesis is feasible. Promise for additional improvements in catalyst performance through application of advanced preparation methods and optimization of catalyst chemical and physical properties is also indicated.

Flow reactor experiments and X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the importance of platinum oxide formation on Pt/BaO/Al₂O₃ NO_x storage catalysts during reactions conditions. The reaction studied was NO(g)  +  1/2 O₂(g) ⇔ NO₂(g). During NO₂ exposure of the catalyst the NO₂ dissociation rate decreased during the reaction. This activity decrease with time was also studied with XPS and it was found to be due to platinum oxide formation. The influence of sulphur exposure conditions on the performance of the NO_x storage catalysts was studied by exposing the samples to lean and/or rich gas mixtures, simulating the conditions in a mixed lean application, containing SO₂. The main results show that all samples are sensitive to sulphur and that the deactivation proceeds faster when SO₂ is present in the feed under rich conditions than under lean or continuous SO₂ exposure. Additionally, the influence of the noble metals present in the catalysts was investigated regarding sulphur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable to retain high performance of the catalyst under SO₂ exposure and subsequent regeneration. Finally, the behaviour of micro-fabricated model NO_x storage catalysts was studied as a function of temperature and gas composition with area-resolved XPS. These model catalysts consisted of a thin film of Pt deposited on one-half of a BaCO₃ pellet. It was found that the combination of SO₂ and O₂ resulted in migration of Pt on the BaCO₃ support up to one mm away from the Pt/BaCO₃ interface.

Here we describe studies of the fine structure of zeolites by TEM started at Cambridge in 1982. These include investigations of coincidence boundaries in LTL, the surface structures of FAU and EMT, the surface structures of LTL and supported metal clusters and the structural relation between MFI and MEL. These, combined with present studies of mesoporous crystals and nanostructured materials demonstrate the strength of electron microscopy in this field of material science.

The CO₂ absorption properties of potassium-based TiO₂ sorbents prepared by calcining at various temperatures from 300 to 700 °C under N₂ and air were investigated in a fixed bed reactor at 60 °C. The CO₂ capture capacity of the sorbent was changed dramatically depending on the structure of the sorbent, which was affected by calcination atmosphere, as well as calcination temperature.

The room temperature adsorption and reaction of CO on Pd(111) surfaces decorated with submonolayer coverages of vanadium oxide – so-called “inverse” model catalysts – have been studied by high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The HREELS surface phonon spectra of the V oxide phases have been measured and used to monitor the changes in the oxide as a result of the interaction with CO. The intramolecular C–O stretching frequency of CO adsorbed on the V-oxide/Pd(111) surfaces displays two vibrational loss components as a function of CO coverage as it has been observed on the clean Pd(111) surface. The relative intensities of the two vibrational features as a function of V oxide coverage however suggest that the balance of CO adsorption sites is modified as compared to clean Pd(111) by the presence of the V oxide–Pd phase boundary. Preferential population of high coordination adsorption sites by CO in the vicinity of the oxide–metal interface is proposed. The analysis of the V oxide phonon spectra indicates that adsorbed CO partially reduces the V oxide at the boundaries of the oxide islands to the Pd metal. The reduction of V oxide by CO is dependent on the oxygen content of the V oxide phase. The reduction of V oxide is confirmed by the XPS V 2p core level shifts.

Amorphous, mesoporous titania–silica mixed oxides with covalently bound mono- and bidentate acetoxyalkyl and aminoalkyl functional groups were prepared using the solution sol–gel process and ensuing low temperature supercritical extraction with CO₂. Titanbisacetylace-tonatediisopropoxide, tetramethoxysilane and amino- or acetoxyalkyl-trimethoxysilane precursors were used for the syntheses of hybrid aerogels with a constant Ti : Si atomic ratio of 1 : 12. The mixed oxides were characterized by thermal analysis, N₂physisorption, ¹³C- and ²⁹Si-CP-MAS NMR spectroscopy, and electron microscopy. The amorphous mesoporous structure of the aerogels depended markedly on the nature of the modifier. Organic modification enhanced remarkably the rate of epoxidation of cyclohexene and cyclohexenol. The highest selectivity in the more demanding epoxidation of cyclohexenol, 91% at 80% TBHP conversion, was achieved with a bidentate (diaminoalkyl)-modified aerogel.

Three model catalysts (Pt/Al₂O₃, Pt/TiO₂, Pt/V₂O₅/TiO₂) were examined in regard to their NO₂ formation ability under a changing lean gas composition. The results show that the NO to NO₂ oxidation function as well as the NO_x reduction under lean gas conditions is affected by a change in the lean gas atmosphere. The NO oxidation activity also decreased with time, for Pt/Al₂O₃ and Pt/TiO₂, and a possible explanation may be platinum oxide formation. This deactivation was not observed for Pt/V₂O₅/TiO₂.