Amine-functionalised hexagonal mesoporous silica as support for copper(II) acetylacetonate catalyst

Copper(II) acetylacetonate was anchored onto a hexagonal mesoporous silica (HMS) material using a two-step procedure: (i) functionalisation of the surface hydroxy groups with (3-aminopropyl)triethoxysilane (AMPTSi) and then (ii) anchoring of the copper(II) complex through Schiff condensation with free amine groups, using two different metal complex loadings. Upon the first step, nitrogen elemental analysis, XPS and DRIFT showed the presence of amine groups on the surface of the HMS material, and porosimetry indicated that the structure of the mesoporous material remained unchanged, although a slight decrease in surface area was observed. Atomic absorption, XPS and DRIFT showed that copper(II) acetylacetonate was anchored onto the amine-functionalised HMS by Schiff condensation between the free amine groups and the carbonyl groups of the copper(II) complex; using EPR an NO3 coordination sphere was proposed for the anchored copper(II) complex. The new [Cu(acac)2]-AMPTSi/HMS materials were tested in the aziridination of styrene at room temperature, using PhI=NTs as nitrogen source and acetonitrile as solvent. The styrene conversion and total TON of the heterogeneous phase reaction are higher than those of the same reaction catalysed in homogeneous phase by [Cu(acac)2]; nevertheless, the initial activity decreases and the reaction time increases due to substrate and product diffusion limitations. The heterogeneous catalyst showed a successive slight decrease in catalytic activity when reused for two more times. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Support-mediated alkane activation over Pt-SO4/Al2O3 catalysts

The development of catalytic materials for the efficient combustion of light alkanes is fundamentally important for both automotive pollution control and the control of emissions produced from bio-fuel combustion. The presence of trace gas-phase SO2 is known to promote low temperature propane combustion over conventional Pt/Al2O3 combustion catalysts, however, there have been no systematic efforts to isolate the respective roles of support and metal, and it remains unclear, which plays the dominant role in this unusual phenomenon. Light alkane combustion over Pt/Al2O3 using pre-sulfated alumina supports to tune the physicochemical catalyst properties was presented. Support sulfation significantly enhanced ethane combustion, and improved methane and propane light-off. Catalyst activity increased with Pt loading, while the magnitude of sulfate promotion scales with alkane chain length. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).

Phonological simplifications, apraxia of speech and the interaction between phonological and phonetic processing

Research on aphasia has struggled to identify apraxia of speech (AoS) as an independent deficit affecting a processing level separate from phonological assembly and motor implementation. This is because AoS is characterized by both phonological and phonetic errors and, therefore, can be interpreted as a combination of deficits at the phonological and the motoric level rather than as an independent impairment. We apply novel psycholinguistic analyses to the perceptually phonological errors made by 24 Italian aphasic patients. We show that only patients with relative high rate (>10%) of phonetic errors make sound errors which simplify the phonology of the target. Moreover, simplifications are strongly associated with other variables indicative of articulatory difficulties - such as a predominance of errors on consonants rather than vowels -but not with other measures - such as rate of words reproduced correctly or rates of lexical errors. These results indicate that sound errors cannot arise at a single phonological level because they are different in different patients. Instead, different patterns: (1) provide evidence for separate impairments and the existence of a level of articulatory planning/programming intermediate between phonological selection and motor implementation; (2) validate AoS as an independent impairment at this level, characterized by phonetic errors and phonological simplifications; (3) support the claim that linguistic principles of complexity have an articulatory basis since they only apply in patients with associated articulatory difficulties.

An investigation of support effects on the Pt-catalysed selective transformation of α,β-unsaturated substrates

Pt catalyst series were prepared on mesoporous SBA-15, SBA-16, KIT-6, true liquidcrystal-templated meso-macroporous SBA-15 and a commercial, low surface area silicasupport. Support structure can be easily fabricated using surfactant templating as a mode ofstringent control on porosity, surface area and internal structure. The impact of varying Pt-support physicochemical properties was systematically studied for the selective transformation of allylic substrates under chemoselective oxidation and hydrogenation regimes, a class of reactions highly applicable to industry. Pt-based heterogeneous catalysts are well-known for their utilisation in the hydrogenation of α,β-unsaturated aldehydes,although the mode of action and lack of systematic studies in the literature fuels continuing debate into the role of Pt nanoparticles and support choice for this area. This project attempts to shed some light on several frequently asked questions in this field. Successful support synthesis and stability after Pt impregnation is confirmed through HRTEM, XRD and N2 porosimetry. Decreasing metal loading promoted dispersion values,regardless of support choice, with surface PtO2 content also showing visible enhancement.Increasing support surface area and mesoporosity exhibited the following trend on Pt dispersion augmentation; low surface area commercial silica < true liquid crystal-templated SBA-15 < SBA-15 < SBA-16 ~ KIT-6. For the selective oxidation of cinnamyl alcohol,increasing PtO2 surface population confers substantial rate enhancements, with turnover frequencies evidencing PtO2 to be the active species .In the Pt-catalysed hydrogenation of cinnamaldehyde, strong support insensitivity was observed towards catalytic activity; as turnover frequencies normalised to Pt metal reveal constant values. However, structure sensitivity to the desired unsaturated alcohol arose,evidencing the requirement of flat, extended Pt (111) facets for C=O hydrogenation. Pt/SBA-15 proved the most selective, reflecting suppressed cinnamyl alcohol hydrogenation, with DRIFTS and in-situ ATR-IR evidencing the key role of support polarity in re-orientation of cinnamaldehyde to favour di-σCO adsorption and C=O versus C=C hydrogenation. High pressures increased activity, whilst a dramatic shift in selectivity from dominant C=C (1 bar)to C=O hydrogenation (10 bar) was also observed, attributed to surface crowding and suppression of di-σCC and η4 di-σCO+πC=C cinnamaldehyde binding modes.