Yongsheng Chen

Thin porous alumina sheets as supports for stabilizing gold nanoparticles.

Thin porous alumina sheets have been synthesized using a lysine-assisted hydrothermal approach resulting in an extraordinary catalyst support that can stabilize Au nanoparticles at annealing temperatures up to 900 °C. Remarkably, the unique architecture of such an alumina with thin sheets (average thickness ~15 nm and length 680 nm) and rough surface is beneficial to prevent gold nanoparticles from sintering. HRTEM observations clearly showed that the epitaxial growth between Au nanoparticles and alumina support was due to strong interfacial interactions, further explaining the high sinter-stability of the obtained Au/Al2O3 catalyst. Consequently, despite calcination at 700 °C, the catalyst maintains its gold nanoparticles of size predominantly 2 ± 0.8 nm. Surprisingly, catalyst annealed at 900 °C retained the highly dispersed small gold nanoparticles. It was also observed that a few gold particles (6-25 nm) were encapsulated by an alumina layer (thickness less than 1 nm) to minimize the surface energy, revealing a surface restructuring of the gold/support interface. As a typical and size-dependent reaction, CO oxidation is used to evaluate the performance of Au/Al2O3 catalysts. The results obtained demonstrated Au/Al2O3 catalyst calcined at 700 °C exhibited excellent activity with a complete CO conversion at ∼30 °C (T100% = 30 °C), and even after calcination at 900 °C, the catalyst still achieved its T50% at 158 °C. In sharp contrast, Au catalyst prepared using conventional alumina support shows almost no activity under the same preparation and catalytic test conditions.

Role of Pentahedrally Coordinated Titanium in Titanium Silicalite-1 in Propene Epoxidation

Two titanium silicalite-1 samples with different crystal sizes were synthesized in the tetrapropylammonium bromide (TPABr) and tetrapropylammonium hydroxide (TPAOH) hydrothermal systems. The small-crystal TS-1 with a size of 600 nm was then treated with different organic bases. These TS-1 samples were evaluated in the epoxidation of propene, and characterized by ultraviolet-visible diffuse reflectance (UV-vis), X-ray absorption near edge structure (XANES) and Raman spectroscopies. The Ti L-edge absorption spectra show that a new Ti species, pentahedrally coordinated Ti, appears in some of the samples. This pentahedrally coordinated Ti species is correlated with the catalytic oxidation activity of TS-1, closely. Tetrahedrally coordinated Ti in TS-1 is the primary active center for selective oxidation reactions, but the existence of a small amount of pentahedrally coordinated Ti can further improve the catalytic activity. A high molar ratio of Si/Ti (n(Si/Ti)) in the synthesis process (n(Si/Ti) = 92.78) was beneficial for the generation of pentahedrally coordinated Ti. The improved catalytic activity of the TPAOH treated TS-1 is mainly due to the increasing amount of pentahedrally coordinated Ti, besides the elimination of diffusion limitation. Slowing down the crystallization rate can also increase the content of pentahedrally coordinated Ti.

Selective oxidation of ethane to aldehydes over SBA-15 supported molybdenum catalyst

Abstract SBA-15 supported Mo catalysts (Mo y /SBA-15) were prepared by an ultrasonic assisted incipient-wetness impregnation method. The physical and chemical properties of the catalysts were characterized by means of N 2 -adsorption-desorption, XRD, TEM, UV-Vis, Raman, XANES and H 2 -TPR. The results showed that a trace amount of MoO 3 was produced on high Mo content samples. Turn-over frequency (TOF) and product selectivity are dependent on the molybdenum content. Both Mo 0.75 /SBA-15 and Mo 1.75 /SBA-15 catalysts give the higher catalytic activity and the selectivity to the total aldehydes for the selective oxidation of C 2 H 6 . At the reaction temperature of 625 °C, the maximum yield of aldehydes reached 4.2% over Mo 0.75 /SBA-15 catalyst. The improvement of the activity and selectivity was related with the state of MoO x species.

Selective catalytic reduction of NO with NH3 over Mo–Fe/beta catalysts: the effect of Mo loading amounts

A series of Mox–Fe/beta catalysts with constant Fe and variable Mo content were synthesized and investigated for selective catalytic reduction (SCR) of NOx with NH3. It was found that the Mo0.2–Fe/beta catalyst exhibited excellent activity, N2 selectivity and preferable resistance to H2O and SO2. The Mox–Fe/beta catalysts were characterized by various analytical techniques. TEM and SEM images showed that the addition of Mo could enhance the dispersion of iron oxides. The results of NH3-TPD and Py-IR indicated that the introduction of Mo resulted in a change of Bronsted acidity, which was associated with high-temperature SCR activity. XPS and XANES results showed that the introduction of Mo resulted in a change of Fe2+ content, which determined the low-temperature activity. DFT calculations showed the strong effects of Mo on the crystal structure, charge distribution and oxygen vacancy formation energy of iron oxides, which further explained the role of Mo in the catalyst behaviors during the SCR process.

An experimental study to evaluate the effects of adding glazed hollow beads on the mechanical properties and thermal conductivity of concrete

Abstract This paper discusses the effects of glazed hollow bead particles on the mechanical properties and thermal conductivity of concrete and the micro appearances of the specimens through the scanning electron microscope. In the experiments, glazed hollow bead was added to the concrete to substitute sands. The amount of glazed hollow bead was kept at 5, 10, 15 and 20% by weight. The results show that the higher the glazed hollow bead amount, the higher will be the percentage of broken glazed hollow bead particles during the mixing process of concrete and that the addition of glazed hollow bead particles reduces the density, compressive strength, elasticity modulus and thermal conductivity coefficient of concrete. When the glazed hollow bead amount reaches 20%, the density, thermal conductivity coefficient, 56-day compressive strength and elasticity modulus of concrete decrease by 14, 69·5, 18·7 and 21·4%, respectively, compared with normal concrete.

Measuring the Unmeasurable by IR Spectroscopy: Carbon Deposition Kinetics in Dry Reforming of Methane

Dry reforming of methane converts two greenhouse gases to syngas, and Ni catalysts are commonly used for this reaction. A major catalyst deactivation mechanism is carbon deposition. Although numerous kinetic modelling works have been performed on carbon formation, there have been only scarce attempts to measure carbon deposition kinetics under relevant (but not real) conditions, owing to technical difficulties. Here, we report the first successful measurements of the kinetics under real reaction conditions. This was made possible by using a novel algorithm that we have developed. We use IR to measure the molar fractions of unreacted CH4 and CO2 , and reaction products, CO and H2 O, in the effluent from the reactor. By applying the general mass balance principle and the relevant reaction stoichiometries, the carbon deposition rate as well as the flow rates of all these gases in the effluent, including H2 , are calculated. Compared to the dominant GC-based approach for catalyst performance evaluation, this method has much higher time resolution and much smaller measurement errors.