Supporting Information

Transcription

1 Supporting Information Copyright Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 2013 A Study of Commercial Nanoparticulate g-al 2 O 3 Catalyst Supports Yahaya Rozita, [a] Rik Brydson,* [a] Tim P. Comyn, [a] Andrew J. Scott, [a] Chris Hammond, [a] Andy Brown, [a] Sandra Chauruka, [a, b] Ali Hassanpour, [b] Neil P. Young, [c] Angus I. Kirkland, [c] Hidetaka Sawada, [d] and Ron I. Smith [e] cctc_ _sm_miscellaneous_information.pdf

2 Determination of General Powder Properties 1. Methods A number of characterisation techniques were employed in order to characterise the γ- Al 2 O 3 powder samples. An AccuPyc 1330 Micromeritics Pycnometer was used to determine the density of ca. 0.5 g of each of the powders by measuring the pressure change of helium in a calibrated volume. BET surface analysis was used to determine the specific surface area of the powders; ca. 0.5g of each sample was degassed at room temperature for 4.5 hours at a low residual pressure (10 p.s.i.) and nitrogen adsorption and desorption isotherms were obtained at liquid nitrogen temperatures using a Micromeritics ASAP-2000 instrument. Specific surface areas were determined using the Brunauer Emmett Teller (BET) method and the particle size, D, was estimated by the equation D (nm) =6 x 10 3 / ( S), where S is the specific surface area and is density. Dynamic light scattering (DLS) detects the fluctuations of the scattering due to the Brownian motion of dispersed nanoparticles and can be used to determine particle size in terms of the hydrodynamic diameter d H in a dispersion. Samples of γ-al 2 O 3 NPs were dispersed in both water (ph 7) and methanol and measured in a 12 µl quartz cuvette on the fixed scattering angle Zetasizer Nano-S system (Malvern Instruments Ltd., Malvern, UK). The samples were measured at room temperature (RT) and the light scattering was detected at 173 o and collected in automatic mode, typically requiring a measurement duration of about 150 seconds. An average of three measurements are reported. The resulting data were analysed using the DTS (version 4.2) software (Malvern Instruments Ltd. Malvern, UK). The Zeta Potential (ZP) is defined as the electrical potential at the surface of shear between the charged surface and the electrolyte; it is employed as an indicator of the electrical force of attraction or repulsion between the surfaces of the particles and hence the stability of colloidal dispersions. For γ-al 2 O 3 NPs, a high zeta potential (typically negative or positive values larger than ±40mV) will confer stability and the dispersion will resist aggregation. When the potential is low, attraction exceeds repulsion and the dispersion will break and flocculate. The ZPs of the colloidal suspensions were determined using a colloidal dynamics zeta probe with an electroacoustic probe which can also measure temperature and conductivity; an automatic titration facility ensured rapid isoelectric point determination as well as the optimum dispersant. Sample preparation for imaging in a Carl Zeiss 1530 Gemini field emission SEM involved grinding the γ-al 2 O 3 NPs in a pestle and mortar and ultrasonically dispersing in methanol for 10 minutes. One drop of this suspension was applied onto a clean aluminium metal stub using a glass pipette; these stubs were then left in air for 20 minutes. A Pt/Pd conductive coating was sputter-coated on top of the samples to prevent charging.

3 2. Results Table S1 summarises the (helium) density values of the dry powders, as well as the values of the zeta potentials (ZP) and DLS peak maxima (as determined by number analysis) for the various samples of γ-al 2 O 3 NPs dispersed in deionised water. Results of the BET surface area, pore volume, pore diameter size and BET particle size for all samples are tabulated in Table S2. Sample AA5 showed an average density value for the dry powder of 3.53 g cm -3 slightly lower than the theoretical value of g cm -3 based on the proposed (cubic) unit cell volume. Most other samples had an average density which was anomalously high which could possibly be due to the sticky nature of the powders forming plugs and/or the presence of adsorbed moisture on the samples. Nitrogen adsorption and desorption isotherms for all powders showed a type v classification after the International Union of Pure and Applied Chemistry (IUPAC), indicating a weak interaction between gas and adsorbent. The BET surface area for sample AA5 was derived to be ± 0.89 m 2 /g (one of the highest of all the samples studied in this work) corresponding to a BET particle size of 7 nm. Pore diameters and pore volumes were also calculated and found to be 15.7 nm (i.e. a mesoporous material) and 1.06 m 3 /g respectively. These values are typical of an agglomerated catalyst support. All the other samples of γ-al 2 O 3 NPs showed a similar pattern for the BET surface (in the range of m 2 /g), BET particle size ( nm), pore volume ( m 3 /g) and pore diameter ( nm). For comparison, Sasol technical data for their sample (SS) gave a surface area of between m 2 /g, a pore volume between m 3 /g and a pore diameter size of 4-10 nm. Figure S1 shows a secondary electron SEM image of the dry AA5 powder indicating the presence of both primary nanoparticles and also agglomerates; EDX confirmed the presence of solely aluminium and oxygen. Very similar results were obtained for all other powders. The agglomerated nature of the dry powders observed by SEM suggests that the measured porosity is interparticle porosity. Although dry powders were heavily agglomerated, they appeared to disperse well in aqueous media. As seen in Table S1, the ZP values for the dispersed samples were all positive which is commonly observed for aqueous γ-al 2 O 3 NP dispersions. AA5 had the highest ZP value (+44.4 mv) indicating a good dispersion stability; most other samples were moderately stable apart from the HT sample which had the lowest ZP value and therefore tended to coagulate. Accordingly, DLS results (Table S1) for sample AA5 exhibited a single primary peak with a maximum intensity at 110 nm (and hence hydrodynamic diameter), similar results being observed for samples AA4 and also SA1. For the remaining samples, DLS showed the presence of both primary and secondary peaks whose maxima lay in the range from a few tens of nanometres up to a few hundreds of nanometres.

4 Sample Zeta Potential (average) Density (average) (g/cm -3 ) DLS peak maxima (nm) as determined by number analysis: p = primary, s = secondary peak. (mv) AA1 23.2± ± (p) and 356 (s) AA2 36.0± ± (p) and 52 (s) AA4 44.2± ± (p) AA5 44.4± ± (p) HT 8.40± ± (p) and 34 (s) JM 24.6± ± (p) and 34 (s) SA1 44.3± ± (p) SA2 37.6± ± (p) and 712 (s) Table S1: Summary of Zeta Potential, Helium Density and DLS measurements Figure S1. SEM secondary electron image of sample AA5

5 Sample BET Surface Area (m 2 /g) BET Particle Size Estimate (nm) Pore Volume Estimate (cm 3 /g) AA ± Pore Diameter Estimate (nm) AA ± AA ± AA ± HT ± JM 58.62± SA ± SA ± Table S2: Summary of BET Surface Area, BET Particle Size, Pore Volume, and Pore Size. No BET particle size is given for HT sample due to a significantly non-spherical morphology.