Insight into the effects of confined hydrocarbon species on the lifetime of methanol conversion catalysts.

The methanol-to-hydrocarbons reaction refers collectively to a series of important industrial catalytic processes to produce either olefins or gasoline. Mechanistically, methanol conversion proceeds through a 'pool' of hydrocarbon species. For the methanol-to-olefins process, these species can be delineated broadly into 'desired' lighter olefins and 'undesired' heavier fractions that cause deactivation in a matter of hours. The crux in further catalyst optimization is the ability to follow the formation of carbonaceous species during operation. Here, we report the combined results of an operando Kerr-gated Raman spectroscopic study with state-of-the-art operando molecular simulations, which allowed us to follow the formation of hydrocarbon species at various stages of methanol conversion. Polyenes are identified as crucial intermediates towards formation of polycyclic aromatic hydrocarbons, with their fate determined largely by the zeolite topology. Notably, we provide the missing link between active and deactivating species, which allows us to propose potential design rules for future-generation catalysts.

Recent advances in automotive catalysis for NOx emission control by small-pore microporous materials.

The ever increasing demand to develop highly fuel efficient engines coincides with the need to minimize air pollution originating from the exhaust gases of internal combustion engines. Dramatically improved fuel efficiency can be achieved at air-to-fuel ratios much higher than stoichiometric. In the presence of oxygen in large excess, however, traditional three-way catalysts are unable to reduce NOx. Among the number of lean-NOx reduction technologies, selective catalytic reduction (SCR) of NOx by NH3 over Cu- and Fe-ion exchanged zeolite catalysts has been extensively studied over the past 30+ years. Despite the significant advances in developing a viable practical zeolite-based catalyst for lean NOx reduction, the insufficient hydrothermal stabilities of the zeolite structures considered cast doubts about their real-world applicability. During the past decade renewed interest in zeolite-based lean NOx reduction was spurred by the discovery of the very high activity of Cu-SSZ-13 (and the isostructural Cu-SAPO-34) in the NH3-SCR of NOx. These new, small-pore zeolite-based catalysts not only exhibited very high NOx conversion and N2 selectivity, but also exhibited exceptionally high hydrothermal stability at high temperatures. In this review we summarize the key discoveries of the past ∼5 years that led to the introduction of these catalysts into practical applications. This review first briefly discusses the structure and preparation of the CHA structure-based zeolite catalysts, and then summarizes the key learnings of the rather extensive (but not complete) characterisation work. Then we summarize the key findings of reaction kinetic studies, and provide some mechanistic details emerging from these investigations. At the end of the review we highlight some of the issues that still need to be addressed in automotive exhaust control catalysis.

Chemical imaging of single catalyst particles with scanning µ-XANES-CT and µ-XRF-CT.

The physicochemical state of a catalyst is a key factor in determining both activity and selectivity; however these materials are often not structurally or compositionally homogeneous. Here we report on the 3-dimensional imaging of an industrial catalyst, Mo-promoted colloidal Pt supported on carbon. The distribution of both the active Pt species and Mo promoter have been mapped over a single particle of catalyst using microfocus X-ray fluorescence computed tomography. X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure revealed a mixed local coordination environment, including the presence of both metallic Pt clusters and Pt chloride species, but also no direct interaction between the catalyst and Mo promoter. We also report on the benefits of scanning µ-XANES computed tomography for chemical imaging, allowing for 2- and 3-dimensional mapping of the local electronic and geometric environment, in this instance for both the Pt catalyst and Mo promoter throughout the catalyst particle.

Determining the storage, availability and reactivity of NH3 within Cu-Chabazite-based Ammonia Selective Catalytic Reduction systems.

Three different types of NH3 species can be simultaneously present on Cu(2+)-exchanged CHA-type zeolites, commonly used in Ammonia Selective Catalytic Reduction (NH3-SCR) systems. These include ammonium ions (NH4(+)), formed on the Brønsted acid sites, [Cu(NH3)4](2+) complexes, resulting from NH3 coordination with the Cu(2+) Lewis sites, and NH3 adsorbed on extra-framework Al (EFAl) species, in contrast to the only two reacting NH3 species recently reported on Cu-SSZ-13 zeolite. The NH4(+) ions react very slowly in comparison to NH3 coordinated to Cu(2+) ions and are likely to contribute little to the standard NH3-SCR process, with the Brønsted groups acting primarily as NH3 storage sites. The availability/reactivity of NH4(+) ions can be however, notably improved by submitting the zeolite to repeated exchanges with Cu(2+), accompanied by a remarkable enhancement in the low temperature activity. Moreover, the presence of EFAl species could also have a positive influence on the reaction rate of the available NH4(+) ions. These results have important implications for NH3 storage and availability in Cu-Chabazite-based NH3-SCR systems.

Correction: Correlation between Cu ion migration behaviour and deNOx activity in Cu-SSZ-13 for the standard NH3-SCR reaction.

Correction for 'Correlation between Cu ion migration behaviour and deNOx activity in Cu-SSZ-13 for the standard NH3-SCR reaction' by A. M. Beale et al., Chem. Commun., 2016, 52, 6170-6173.

5D operando tomographic diffraction imaging of a catalyst bed.

We report the results from the first 5D tomographic diffraction imaging experiment of a complex Ni-Pd/CeO2-ZrO2/Al2O3 catalyst used for methane reforming. This five-dimensional (three spatial, one scattering and one dimension to denote time/imposed state) approach enabled us to track the chemical evolution of many particles across the catalyst bed and relate these changes to the gas environment that the particles experience. Rietveld analysis of some 2 × 106 diffraction patterns allowed us to extract heterogeneities in the catalyst from the Å to the nm and to the µm scale (3D maps corresponding to unit cell lattice parameters, crystallite sizes and phase distribution maps respectively) under different chemical environments. We are able to capture the evolution of the Ni-containing species and gain a more complete insight into the multiple roles of the CeO2-ZrO2 promoters and the reasons behind the partial deactivation of the catalyst during partial oxidation of methane.

Correlation between Cu ion migration behaviour and deNOx activity in Cu-SSZ-13 for the standard NH3-SCR reaction.

Here we present the results of a synchrotron-based in situ, time-resolved PXRD study during activation of two Cu-SSZ-13 catalysts under O2/He and one during standard NH3-SCR reaction conditions to obtain insight into the behaviour of Cu ions. The results obtained indicate that deNOx activity is inexorably linked with occupancy of the zeolite 6r.

3D chemical imaging in the laboratory by hyperspectral X-ray computed tomography.

We report the development of laboratory based hyperspectral X-ray computed tomography which allows the internal elemental chemistry of an object to be reconstructed and visualised in three dimensions. The method employs a spectroscopic X-ray imaging detector with sufficient energy resolution to distinguish individual elemental absorption edges. Elemental distributions can then be made by K-edge subtraction, or alternatively by voxel-wise spectral fitting to give relative atomic concentrations. We demonstrate its application to two material systems: studying the distribution of catalyst material on porous substrates for industrial scale chemical processing; and mapping of minerals and inclusion phases inside a mineralised ore sample. The method makes use of a standard laboratory X-ray source with measurement times similar to that required for conventional computed tomography.

Real time chemical imaging of a working catalytic membrane reactor during oxidative coupling of methane.

We report the results from an operando XRD-CT study of a working catalytic membrane reactor for the oxidative coupling of methane. These results reveal the importance of the evolving solid state chemistry during catalytic reaction, particularly the chemical interaction between the catalyst and the oxygen transport membrane.

A sheep model for MPTP induced Parkinson-like symptoms.

Administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) causes behaviors reminiscent of idiopathic Parkinson's disease in man and other primates, but development of such symptomology has not been reported to date in other species. We now report a sheep model which responds to administration of low levels of the compound with well defined, apparently permanent symptomology very similar to that seen in primates. Histological examination indicates drug dependent destruction of the substantia nigra which, in sheep, lacks the high levels of neuromelanin present in primates. Following infusion of either MPTP or MPP+, only the metabolite MPP+ was detected in serum with this metabolite demonstrating a very long half life. The rapid disappearance of MPTP suggests that its potency will be directly related to a function of body size and inversely related to heart rate.

Effects of oral and parenteral selenium supplements on residues in meat, milk and eggs.

Oral and parenteral preparations of Se are used worldwide to prevent and treat nutritional muscular dystrophy and other Se deficiency syndromes. There are extensive published data on the effects of oral supplementation on Se residues in food animal products. Very little published data exist on the effects of parenteral administration on Se residues, even for cattle and swine in which parenteral preparations are used extensively. The distribution of Se into kidney and liver appears to be equivalent for both forms of supplementation. Elimination of Se in milk is greater after parenteral administration and correlates with high plasma Se levels, however the milk excretion drops quickly and after 4 d returns to control levels (Little et al. 1979). Of particular interest is the finding that up to 18% of Se in an oral diet may be excreted in milk (Maus et al. 1980). Use of Se supplements in poultry results in increased levels of Se in liver, kidney, and eggs. Distribution of Se into liver and kidney is much greater than into breast muscle indicating a greater capacity of these organs to accumulate Se. Excretion of Se into eggs results in Se levels equivalent to those in liver and kidney, indicating that eggs are an important route of Se excretion in laying hens (Ort and Latshaw 1978). When Se supplementation stops, the liver, kidney, and egg white and yolk residues decline quickly to control values within 1-2 wk. Breast muscle Se content changes little during supplementation and after withdrawal of supplementation. Oral and parenteral selenium supplementation in swine result in greater accumulation of Se in liver and kidney than in muscle. Oral selenium supplementation also increases the excretion of Se into milk. This method has been used to prevent Se deficiency disease in piglets (Mahan et al. 1975). Oral supplementation with 0.1 ppm Se, as sodium selenate, did not result in levels of Se in blood, meat, or viscera at slaughter (Jenkins and Winter 1973). Despite the large amount of data available on Se residues in food animals, additional information on the pharmacokinetics of parenterally administered Se preparations is needed, especially in sheep and goats which receive parenteral Se supplements. Information on the disappearance kinetics of Se residues in meat and milk is needed for all ruminants. The data currently available in the literature does not allow the calculation of pharmacokinetic parameters of Se in any species. Properly performed pharmacokinetic studies would contribute a great deal towards a better understanding of how food animals utilize supplemental selenium.(ABSTRACT TRUNCATED AT 400 WORDS)

MPTP-induced Parkinson-like disease in sheep: clinical and pathologic findings.

Eight ewes, divided into two groups based on age, with group 1 7-8 and group 2 1-3 years old, respectively, were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intravenously (IV) at cumulative doses of 2.0 to 34.6 mg/kg body weight. Two group 1 sheep, given cumulative doses of 2 and 8.5 mg/kg, developed persistent severe neurologic signs of body stiffness and rigidity, paucity of movement, intention body tremors, and abnormal body posture and stance similar to those signs in MPTP-induced disease in people and primates. After their acute onset, these persistent signs were nonprogressive up to the observation period of 32 days post infusion. None of the younger ewes had persistent neurologic symptoms at equivalent cumulative doses (9.0 mg/kg). The only pathologic changes were microscopic lesions in the central nervous system, consisting of bilaterally symmetrical neuronal chromatolysis and necrosis limited to the substantia nigra and locus ceruleus. These lesions were found in two persistently affected and two younger sheep, suggesting age-based differences in dose response and the threshold of clinical expression of disease. Serum MPTP half-life was 11 days. Thus sheep exposed to MPTP could be an alternative model to the primate for the comparative study of clinical, pathologic, and biochemical mechanisms in MPTP neurotoxicity and Parkinson's disease in people.

A rapid lead test: public outreach and testing to detect leachable lead in ceramic ware.

A modification of the U.S. Food and Drug Administration (FDA) lead screening test of ceramic ware was made to screen large numbers of samples in a short time frame. Ceramic ware in use by Davis and Sacramento, California residents was tested. Lead was leached from ceramic ware with citric acid and identified by rhodizonic acid in this quick, qualitative test. Of 92 individual pieces of pottery tested, approximately 6.6% were positive for leachable lead. Approximately 67% of the positive samples were handmade in Mexico. This rapid test is sensitive to two (2) parts per million (ppm, microgram/g) leachable lead. Ceramic ware with detectable leachable lead levels may present a health risk to individuals who habitually use such items for food storage and/or consumption. Because only 20-30 minutes is needed to perform the test, immediate communication of results to the participant is possible.

What is the value of measuring renal parenchymal thickness before renal biopsy?

Reduced renal length is widely used to diagnose chronicity in patients with renal impairment. A length of 9 cm or less measured ultrasonographically is considered to indicate irreversible disease. However, some patients with normal renal length have thin parenchyma. The aim of this study was to determine the relationship between ultrasonographically measured parenchymal thickness and renal length and to correlate parenchymal thickness with the histology obtained at renal biopsy. Sixty-four patients, aged 16-74 years, who had had a renal biopsy were evaluated retrospectively. Histology was considered in five categories: I, interstitial nephritis (n = 13); II, glomerulonephritis (28); III, diabetes mellitus/metabolic/other (8); IV, chronic renal disease (CRD) (11); V, hypertension/vascular disease (4). There was a good linear correlation between renal length and renal parenchymal thickness (r = 0.64, P < 0.001). Both were reduced most in patients with CRD. Sixty-four per cent of patients with CRD had renal parenchymal thickness 1.5 cm or less, compared to 38% in group I, 25% in groups II and V, and 7% in group II. Although 11/37 (30%) of patients whose serum creatinine had increased 3 months post-biopsy had parenchymal thickness 1.5 cm or less, so did 6/27 (23%) whose creatinine decreased. Like renal length, parenchymal thickness gives an indication of the chronicity of renal failure. However, some patients with parenchymal thickness 1.5 cm or less still have potential for improvement. This measurement alone should not be used to obviate renal biopsy.