Photochemistry down under: solar chemicals from and for the tropics

The Applied and Green Photochemistry Group at James Cook University (JCU) in Townsville, Australia, has been at the forefront of solar photochemical research and has realized solar transformations from laboratory through to production scales. Located in tropical North Queensland, Townsville experiences over 300 days of sunshine per year, which makes it a favorable location for solar research. The current Solar Chemicals from and for the Tropics initiative of the group builds on both of tropical Australia's abundant natural resources, sunlight and biomass, and utilizes these for the bulk production of commercially and tropically relevant chemicals

Solar chemicals from and for tropical Australia

[Extract] At James Cook University (JCU) in Townsville, Australia, the Applied and Green Photochemistry Group utilizes both of tropical North Queensland's abundant natural resources: sunlight and biomass. The Solar Chemicals from and for the Tropics activities of the group subsequently focus on the production of commercially important commodity chemicals from these materials

Kinetik mittels IR-Spektroskopie: Aktivierung von H2 und D2 an Ag/SiO2-Hydrierkatalysatoren

Kinetik mittels IR-Spektroskopie: Aktivierung von H2 und D2 an Ag/SiO2-Hydrierkatalysatoren F.C. Jentoft,1 J. Kröhnert,1 K. Klaeden,1 R. Schlögl1 M. Bron,2 P. Claus2 1Abteilung Anorganische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin 2Ernst-Berl-Institut für Technische und Makromolekulare Chemie, TU Darmstadt, Petersenstr. 20, 64287 Darmstadt SiO2-geträgerte Ag-Katalysatoren können für die Selektivhydrierung von α,β-ungesättigten Aldehyden zu ungesättigten Alkoholen eingesetzt werden [1,2]. Es ist noch ungeklärt, an welchen Zentren und auf welche Weise der Wasserstoff aktiviert wird. Wir haben die Reaktion von H2 und D2 mit dem reinen Träger SiO2 und einem 9 Gew.% Ag enthaltenden Katalysator IR-spektroskopisch verfolgt. Freitragende Preßlinge wurden bei 325°C im H2-Strom aktiviert, im Vakuum auf Reaktionstemperatur (100-250°C) abgekühlt und 100 mbar D2 (H2) ausgesetzt. Zeitaufgelöst aufgenommene Transmissions-IR-Spektren zeigten, daß die OH-Gruppen des SiO2 zu OD-Gruppen austauschten. Der Austausch ging für die Ag-haltige Probe stets schneller vonstatten. Die Kinetik der Reaktion ließ sich aus der am Anfang linearen Zunahme der OD-Banden verfolgen. Aus der Temperaturabhängigkeit der scheinbaren Geschwindigkeitskonstanten errechneten sich Aktivierungsenergien von ca. 28 kJ/mol für Ag/SiO2 und ca. 38 kJ/mol für SiO2. Der Rücktausch der OD-Gruppen mit H2 zu OH-Gruppen war erheblich langsamer. Für SiO2 bei 200°C betrug das Verhältnis der Geschwindigkeitskonstanten kD/kH ≈ 2. Dieser kinetische Isotopeneffekt weist darauf hin, daß die Spaltung der OH-Gruppe und nicht die Spaltung des Wasserstoffmoleküls geschwindigkeitsbestimmend ist. Die Untersuchungen liefern das etwas überraschende Ergebnis, daß Wasserstoff unter den Bedingungen der Hydrierkatalyse an SiO2 aktiviert (gespalten) werden kann. Der genaue Einfluß des Silbers auf diese Reaktion und die Aktivierung des ungesättigten Aldehyds sind Gegenstand weiterer Untersuchungen. [1] P. Claus, H. Hofmeister, J. Phys. Chem. B 103 (1999) 2766-2775. [2] P. Claus, P.A. Crozier, P. Druska, Fresenius J. Anal. Chem. 361 (1998) 677-679

Labile sulfate species as key active components in sulfated zirconia for activating n-butane

Sulfated zirconia and other sulfated metal oxides have been studied for over 2 decades owing to their high catalytic activity for activation of short alkanes at low temperature. The surface structure of sulfated zirconia has been studied widely in order to elucidate the nature of active sites since the discovery of its catalytic property for alkanes conversion at low temperature. Nevertheless, no consensus has been reached so far. Here, we report that the labile sulfate, which can be removed from sulfated zirconia by water washing, acts as crucial component for the active site of sulfated zirconia. Experimental Sulfate-doped zirconium hydroxide was obtained from Magnesium Electron, Inc. (XZO 1077/01), which was heated up to 873 K with a ramp rate of 10 K/min in static air and kept at 873 K for 3 h, denoted as SZ. Water washing technique was applied to the above calcined sulfated zirconia. 20 g of SZ were suspended in 400 mL bi-distilled water and then filtered. Repeated the washing procedure for 3 times, then the cake was dried at room temperature. The resulting powder is denoted as SZ-WW. The materials were characterized by IR spectroscopy, (including the sorption of probe molecules such as pyridine and CO2), TAP measurements, XRD and the sulfate content was determined. n-Butane isomerization reactions were carried out in a quartz micro tube reactor under atmospheric pressure. Prior to the reaction, the catalyst was activated at 473 K for 2 h in He flow (10 ml/min). Results and Discussion The calcined sulfated zirconia, SZ, showed a catalytic activity of 0.015 mol/g/s for n-butane skeletal isomerization with an initial iso-butane selectivity of 96 % at 373 K. It is interesting to note that the removal of water soluble sulfate by water washing treatment of the parent sample resulted in an inactive sample (SZ-WW). The content of sulfate of the water washed sample (SZ-WW) is 0.25 mmol/g, which is much lower than that of the original calcined sulfated zirconia, 0.44 mmol/g. Thus, 43 % of the total sulfate of sulfated zirconia was removed by water washing. The water washing treatment not only removed the water soluble sulfate of SZ, but also the Brønsted acid sites leading to an increase of Lewis acid concentration. The IR spectra of water washed sulfated zirconia (SZ-WW) and sulfated zirconia (SZ) samples showed pronounced difference in the region OH and S=O vibrations. In the IR region of OH group above 3600 cm-1, water washing increased the intensity of the OH band at 3634 cm-1 and shifted it to higher frequency, 3661 cm-1. In addition, water washing reduced a fraction of sulfate groups at high frequency leading to sulfate stretching vibrations of water washed sample (SZ-WW) at 1391 cm-1 compared to the parent sample (SZ) at 1404 cm-1. Note that the wavenumber of the S=O stretching vibration is related to the SO bond order [ , ], indicating that fractions of highly covalent sulfate were removed. IR spectra recorded during adsorption of CO2 showed the formation of bicarbonate on the surface of the washed sample but not on the original sample. SZ-WW featured an about equal number of two different types of Lewis acid sites, while for SZ one type of Lewis acid sites was predominant. The data indicate that water washing produces domains of bare zirconia surface, free of sulfate. The results show for the first time that the water soluble sulfate species are responsible for the formation of highly covalent sulfates as well as the Brønsted acid sites, which are essential for the alkane isomerization reaction on sulfated zirconia at low temperature. Elementary steps are discussed based on steady state and transient kinetic measurements