The Promotional Effects of ZrO2 and Au on the CuZnO Catalyst Regarding the Durability and Activity of the Partial Oxidation of Methanol

The promoter ZrO2 was applied to prevent Cu crystallites from sintering over CZ (ca. Cu 30 wt.% and Zn 70 wt.%) under partial oxidation of the methanol (POM) reaction. Gold was selected to promote the performance of CZrZ (ca. Cu 31 wt.%, Zr 16 wt.%, and Zn 53 wt.%) catalyst to overcome a high ignition temperature of 175 °C and CO selectivity (SCO) (>10% at T. > 200 °C). Experimentally, the deactivation rate constant of A5CZrZ (ca. Au 5 wt.%, Cu 31 wt.%, Zr 17 wt.%, and Zn 47 wt.%) and CZrZ was 1.7 times better than A5CZ (ca. Au 5 wt.%, Cu 31 wt.%, and Zn 64 wt.%) and CZ. The methanol conversion of CZrZ and A5CZrZ catalysts was kept higher than 70% for 12 h in an accelerated aging process. Meanwhile, the Au prompted more methoxy species oxidizing to formate on Cu+-rich A5CZrZ surface at lower temperature, and also improved CO transfer from formate reacting with moveable oxygen to form CO2. The SCO can lower to ca. 6% at 200 °C after adding 3–5% of gold promoter. These features all prove that the CZ catalyst with ZrO2 and Au promoters could enhance catalytic activity, lower the SCO and ignition temperature, and maintain good durability in the POM reaction.

Atomic Layer Deposition for Improved Stability of Catalysts for the Conversion of Biomass to Chemicals and Fuels

ABSTRACTAtomic layer deposition (ALD) has been used to coat SBA-15 and functionalized SBA-15 with various metal oxides. Use of SBA-15 coated with 4-10 ALD cycles of titania, alumina, niobia, or zirconia in the acid-catalyzed dehydration of fructose to 5-hydroxymethylfurfural (HMF) resulted in 24-57% conversion, with 0-22% selectivity, at 130 °C with 2 wt % fructose in 4:1 THF:H2O. Propylsulfonic acid functionalized SBA-15 (SBA-15-PrSO3H) had a 25% conversion and 48% selectivity for HMF under the same conditions. SBA-15-PrSO3H was also coated with 2 ALD cycles of titania followed by 8 ALD cycles silica. The deactivation rate constant for SBA-15-PrSO3H was 2.7 x 10-2 h-1 for the dehydration of fructose to HMF in a flow reactor at 130 °C with a feed of 2 wt % fructose in 4:1 THF:H2O. In comparison, the deactivation rate constant for the ALD coated SBA-15-PrSO3H-ALD was 7.9 x 10-3 h-1.

Hydrogenation of Acetylene: Kinetic Studies and Reactor Modeling

The kinetics of acetylene hydrogenation has been studied in a fixed bed reactor of a commercial Pd/Al2O3 catalyst. The experiments were carried out at 30, 50 and 70 ºC with various feed compositions at atmospheric pressure. The experiments were repeated at 70 ºC in the presence of the used catalyst to determine the effect of the catalyst deactivation where the corresponding deactivation rate constant was determined in order to predict the activity of the catalyst during each run. Two well known kinetic models were used for a nearly similar catalyst to predict the experimental data of this work and none of them were found satisfactory. A new model was then proposed to fit the experimental data. The hydrogenation reactor was also simulated at industrial operating conditions with the proposed kinetics for both plug and dispersion flows. The results of these simulations were almost close to each other in most cases.

The role of the C-terminal tail of flavocytochrome b2

A flavocytochrome b2 (L-lactate dehydrogenase) mutant was constructed in which the C-terminal tail (23 amino acid residues) had been deleted (Gly-489→Stop). This tail appears to form many intersubunit contacts in the tetrameric wild-type protein, and it was expected that its removal might lead to the formation of monomeric flavocytochrome b2. The isolated tail-deleted mutant enzyme (TD-b2), however, was found to be tetrameric (Mr 220,000). TD-b2 shows Km and kcat. values (at 25 degrees C and pH 7.5) of 0.96 +/- 0.06 mM and 165 +/- 6 s-1 respectively compared with 0.49 +/- 0.04 mM and 200 +/- 10 s-1 for the wild-type enzyme. The kinetic isotope effect with [2-2H]lactate as substrate seen for TD-b2, with ferricyanide as electron acceptor, was essentially the same as that observed for the wild-type enzyme. TD-b2 exhibited loss of activity during turnover in a biphasic process. The rate of the faster of the two phases was dependent on L-lactate concentration and at saturating concentrations showed a first-order deactivation rate constant, kf(deact.), of 0.029 s-1 (at 25 degrees C and pH 7.5). The slower phase, however, was independent of L-lactate concentration and gave a first-order deactivation rate constant, ks(deact.), of 0.01 s-1 (at 25 degrees C and pH 7.5). This slower phase was found to correlate with dissociation of FMN, which is one of the prosthetic groups of the enzyme. Thus fully deactivated TD-b2, which was also tetrameric, was found to be completely devoid of FMN. Much of the original activity of TD-b2 could be recovered by re-incorporation of FMN. Thus the C-terminal tail of flavocytochrome b2 appears to be required for the structural integrity of the enzyme around the flavin active site even though the two are well separated in space.

Collisional Deactivation Rates of Electronically Excited Molecular Ions. II

Total deactivation rate constants have been determined for N2+(B2Σu+) and the (A2Πu) and (B2Σu+) states of CO2+ with a number of quenchers. The energy specific total deactivation rate constant is compared to the total radiative lifetime of the excited species. A particular novelty of the technique is that it does not require a complete knowledge of the formation modes for the excited species. The results are compared with theoretical values obtained from the ion-induced dipole model. Individual deactivation rate constants are presented for N2+(B2Σu+) ions in the v = 0, 1, and 2 vibrational levels quenched by N2, O2, H2, and CO2; and for the(A2Πu) and (B2Σu+) states of CO2+ quenched byCO2, N2, O2, NO, and H2. Charge transfer is the most probable mode of deactivation except in the CO2+–H2 reactions where H-atom abstraction is more probable.