Enhancement of immobilized enzyme activity by pretreatment of β-glucosidase with cellobiose and glucose

In this study, β-glucosidase from Aspergillus niger was pretreated with cellobiose and glucose to prevent loss of enzyme activity, and pretreated β-glucosidase was immobilized on silica gel as a carrier by covalent binding. To enhance the activity of immobilized β-glucosidase, the effects of substrate concentration and reaction conditions, including temperature, time, and agitation speed, were investigated. The optimal concentrations of cellobiose and glucose, temperature, time, and agitation speed were determined to be 0.02 M, 40 °C, 20 min, and 130 rpm, respectively. The activity of immobilized β-glucosidase after pretreatment was increased to about 176% of that of non-pretreated β-glucosidase. In addition, the optimal pH and temperature of the non-pretreated and pretreated immobilized β-glucosidases were both pH 5.5 and 65 °C, respectively. Moreover, the immobilized β-glucosidases were used repeatedly 20 times, and the enzyme activities were maintained at levels higher than 80% of their initial activities.     

Broadening of the effective temperature range for NO removal on Co·Pd-modified H-ZSM-5 catalyst by suppression of CH4 combustion

Broadening the effective temperature range (window) of NO removal on Co·Pd-modified H-ZSM-5 (Co/Pd/H-ZSM-5) in the presence of methane under an excess-oxygen condition was tried under the concept that the lack of the amount of methane occurred by CH₄ combustion at high temperature reduced NO conversion to N₂. The activity for NO removal of the catalyst at high temperature was improved due to suppression of methane combustion by the thermal treatment of Pd in a H₂-containing flow. Co/Pd/H-ZSM-5s with and without the thermal treatment of Pd showed different temperature windows for NO elimination. These different windows were then combined by a two-stage catalyst packing, in which Co/(Pd/H-ZSM-5)_red. and Co/Pd/H-ZSM-5 were placed in series, resulting in the broadening of the window. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design criteria for high‐temperature combustion catalysts

In this paper design criteria used in the development of new highly active materials for high‐temperature catalytic combustion of natural gas are presented with selected examples. It is the composition and structure of a given material which determine the activity. Specific surface area plays a secondary role. This revised version was published online in July 2006 with corrections to the Cover Date.     

The formation of HCN during the reduction of NO by isobutane over Fe‐MFI made by solid‐state ion exchange

FTIR analysis of the gaseous products of the selective catalytic reduction of NO by isobutane over a Fe‐MFI catalyst made by solid‐state ion exchange shows, for the first time, that HCN can be a substantial product. Under dry conditions the amounts formed can exceed that of N₂ for temperatures up to 280°C and NO conversions of 25% with a maximum HCN concentration of∼150 ppm formed at 315°C. However, introduction of 0.7% water causes the subsequent conversion of about one‐half the HCN to N₂, probably through hydrolysis to NH₃ and the NH₃‐SCR reaction which is very rapid on Fe‐MFI. The steps through which HCN forms remain to be established. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhancement of mechanical strength and osteogenesis,and inhibition of osteoclastic activity for β-tricalcium phosphate bioceramics by incorporating calcium silicate and magnesium-strontium phosphate

β-tricalcium phosphate bioceramics suffer from a drawback of poor mechanical strength and a scarcity of capacity to regulate biological performances. In the current study, the overall performances of β-tricalcium phosphate (TCP) bioceramics were improved by incorporating calcium silicate (CS) and magnesium-strontium phosphate (MSP). During the sintering process, the MSP stabilized the β phase of TCP, and the formation of MSP melt ensured effective liquid-sintering of TCP, thus conducing to lower porosity of TCP/MSP and TCP/CS/MSP bioceramics. In comparison with the TCP bioceramics, the TCP/CS and TCP/MSP bioceramics showed lower compressive strength, while the TCP/CS/MSP bioceramics attained noticeably higher compressive strength. Due to the sustained release of therapeutical ions, the TCP/CS bioceramics enhanced in vitro early-stage osteoblastic differentiation, but compromised cell proliferation; both the TCP/MSP and TCP/CS/MSP bioceramics enhanced cell proliferation and osteoblastic differentiation, and restrained osteoclastic activities. Collectively, the TCP/CS/MSP bioceramics with optimal overall performances are promising for efficaciously treating the defects of osteoporotic bone.     

Lean selective catalytic reduction of NO2 by methane over Co‐zeolites

The reaction of NO₂, CH₄ and O₂ was studied using low levels of methane compared to NO₂ and O₂ over protonic and cobalt‐exchanged ferrierite, ZSM‐5 and mordenite zeolites. Results suggest that two reaction pathways at low and high temperatures may be involved in the lean selective catalytic reduction (SCR) of NO₂ by methane. At low temperatures, the reduction of NO₂ to NO and N₂ might be the initial reaction step. It is likely that NO₂ or its adsorbed precursors initiate the reaction of methane at low temperatures. At high temperatures, the oxidation of NO and combustion of methane with oxygen might be involved. No appreciable differences were observed in the reduction of NO₂ over Co‐zeolites as compared to known results of NO reduction over these materials. However, enhanced N₂ formation rate was observed on H‐zeolites starting from NO₂ instead of data reported for NO. Furthermore, it appears that the active sites for SCR are both acid and metal sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

On‐line addition of catalyst in high‐temperature reactors: high selectivity to olefins

By adding solutions containing catalyst salts to hot monolith catalysts during partial oxidation processes, the salt decomposes instantly and is deposited selectively near the front face. We have used this technique to deposit extremely small amounts of Pt on α-Al₂O₃ monoliths during ethane oxidation to olefins. We find that on this catalyst with H₂ addition, the selectivity to ethylene rises from ∼ to over 80% at an ethane conversion of ∼60% and at complete O₂ conversion. We also examine the addition of promoters including Sn, which gives improved performance compared to the Pt catalyst alone. This appears to be a general effect that could be useful in preparing catalysts with different loadings and distributions in high‐temperature processes. It can also be used for rapid and accurate diagnosis of catalysts and additives and to modify catalysts on‐line in situations where deactivation or catalyst loss occurs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of silver on the catalytic activity of Cu‐ZSM‐5 for NO SCR by propane. Effect of the presence of water and hydrothermal agings

The effect of silver on the activity and hydrothermal stability of Cu‐ZSM‐5 for NOχ reduction with C₃H₈ under oxidizing and wet conditions has been investigated. The addition of silver as a cocation to Cu‐ZSM‐5 catalysts decreases the reversible inhibition by water occurring under catalytic conditions when the temperature does not exceed 773 K. Furthermore, it suppresses the irreversible deactivation observed when the reaction is performed up to 873 K. In effect, the Cu–Ag‐ZSM‐5 solids are more resistant to the dealumination induced by the acids formed by reactions between NO, O₂ and H₂O than the Cu‐ZSM‐5 ones. The presence of silver provides also an higher hydrothermal stability under an (air + 10 vol% H₂O) mixture if the temperature does not exceed 973 K. The catalytic activity and the deactivation behaviour are dependent on the concentration of silver and copper and more especially on the preparation procedure. This revised version was published online in July 2006 with corrections to the Cover Date.     

An in situ infrared study of NO reduction by C3H8 over Fe‐ZSM‐5

The interactions of NO, O₂ and NO₂ with Fe‐ZSM‐5, as well as the reduction of NO by C₃H₈ in the presence of O₂, have been investigated using in situ infrared spectroscopy. The sample of Fe‐ZSM‐5 (Fe/Al =0.56) was prepared by solid‐state ion exchange. NO adsorption in the absence of O₂ produces only mono‐ and dinitrosyl species associated with Fe²⁺ cations. Adsorbed NO₂/NO₃ species are formed via the reaction of adsorbed O₂ with gas‐phase NO or by the adsorption of gas‐phase NO₂. The reduction of NO in the presence of O₂ begins with the reaction of gas‐phase C₃H₈ with adsorbed NO₂/NO₃ species to form a nitrogen‐containing polymeric species. A reaction pathway is proposed for the catalyzed reduction of NO by C₃H₈ in the presence of O₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

Porous Mn–Co mixed oxide nanorod as a novel catalyst with enhanced catalytic activity for removal of VOCs

Mn–Co mixed oxide nanorod with porous structure and high surface area was fabricated by an oxalate route and further used for deep oxidation of VOCs. Compared to the single MnO_x or Co₃O₄, the Mn–Co mixed oxide showed an enhanced activity for ethyl acetate and n-hexane oxidation with T_90% was low to 194 and 210 °C at a high space velocity, respectively. The formation of solid solution with spinel structure inhibits the growth of nanoparticles which leads to its higher surface area, and the strong synergistic effect of Mn–Co species in the oxide makes a great contribution to its low temperature reducibility which plays a key role in VOCs' oxidation.     

Rapid synthesis of small crystal FeZSM‐5 by a two‐stage varying‐temperature technique

Small crystal FeZSM‐5 was synthesized by a two‐stage varying‐temperature technique, in which the reaction mixture was first kept at a relatively low temperature for a period, and then abruptly raised to the required crystallization temperatures. The effects of sol concentration, alkalinity, temperature as well as templates on crystal size were investigated. The results showed that the crystal size of the ultimate product could be tailored through controlling the nucleation period and rate in the first stage via changing alkalinity, templates, and water content in hydrogel. Typically, a product with uniform crystal size of about 300 nm was obtained from a reaction mixture with molar ratio 1SiO₂ : 0.02Fe₂O₃ : 0.6R : 0.3Na₂O : 50H₂O (R = n‐butylamine) under suitable crystallization conditions for 50 h. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of framework aluminum in proton‐ or copper‐exchanged MFI ferrialuminosilicates on their activity for the reduction of nitric oxide with ammonia

Reduction of NO with ammonia in excess oxygen has been carried out on protonform and Cu²⁺exchanged MFI ferrialuminosilicate. Though HZSM5 showed very low activity, the framework Al in Hferrialuminosilicate greatly enhanced the activity. The framework Al in Cu²⁺exchanged ferrialuminosilicate also enhanced the activity to some extent.     

The colloidal synthesis of unsupported nickel‐tin bimetallic nanoparticles with tunable composition that have high activity for the reduction of nitroarenes

Ni‐Sn bimetallic nanoparticles with controllable size and composition were prepared by facile method in ambient air using inexpensive metal salts. Adjusting stoichiometric ratio of Ni and Sn precursors afforded nanoparticles with different compositions, such as Ni₁₀₀, Ni₇₄‐Sn₂₆, Ni₅₉‐Sn₄₁, and Ni₅₀‐Sn₅₀. The characterization of nanoparticles was performed by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), and energy dispersive X-ray analysis (EDX). Ni₇₅‐Sn₂₅ and Ni₆₀‐Sn₄₀ nanoparticles showed enhanced catalytic activity towards 2-nitroaniline reduction as compared with Ni nanoparticles. Furthermore, Ni₇₅‐Sn₂₅ nanocatalyst exhibited excellent activity for the reduction of a number of nitro aromatic compounds under mild conditions along with high level of reusability.     

Fabrication and characterization of the Ag‐based high‐technology model nanocluster catalyst for ethylene epoxidation manufactured by electron beam lithography

Nanocluster catalysis is an area where greater fundamental knowledge is needed to understand the behavior of aggregates of metal atoms in determining product selectivity of chemical reactions. While catalysis is practiced industrially with economic success there is still a great need to eliminate wasteful sidereactions which hurt overall yields. Here we report on fabrication of a Agbased hightechnology model nanocluster catalyst by using electron beam lithography (EBL) designed for systematic studies of the ethylene epoxidation reaction. The catalyst is made of a square array of cylindershaped Ag nanoclusters that are 200 Å in diameter, deposited on a four inch silicon wafer, precovered with a 100 Å thick film of alumina. The height of the particles and interparticle distance can vary, and were chosen to be 150–300 and 1000 Å, respectively. The high technology catalyst was characterized by Xray photoelectron spectroscopy (XPS), highresolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The thermal stability of Ag nanoclusters in vacuo was investigated.     

Synergistic Enhancement of the Extraction of Trivalent Lanthanides and Actinides by Tetra‐(n‐Octyl)Diglycolamide from Chloride Media

Abstract

This work describes a unique synergistic enhancement of the extraction of trivalent actinides and lanthanides by extraction chromatographic resins containing tetra‐n‐octyldiglycolamide (TODGA) from hydrochloric acid containing anionic metal chlorides. The presence of mg/L quantities of trivalent Fe, Ga, In, Tl, or Bi in HCl leads to several orders of magnitude enhancement of the extraction of trivalent actinides and lanthanides. The synergistic effect persists, even when the amount of metal chloride exceeds the capacity of the resin. The application of this synergistic enhancement for the separation of actinium from stainless steel and the preconcentration of americium and plutonium from large soil samples will be described.     

High activity and stability of the Rh‐free Co‐based ex‐hydrotalcite containing Pd in the catalytic decomposition of N2O

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over calcined hydrotalcite‐like compounds containing different combinations of bivalent (Co, Pd, Mg) and trivalent (Al, La, Rh) cations with carbonate as interlayer anion. The precursors were prepared by co‐precipitation under low supersaturation conditions and characterized by XRD and TG/DSC. The mixed oxides derived after calcination at 723 K were characterized by XRD, N₂ adsorption at 77 K, and XRF. The presence of Rh, La, or Pd in the Co‐based HTlc's improves considerably the catalytic activity. Co–Rh,Al‐HTlc (Co/Rh/Al==3/0.02/1) proved to be a very active catalyst, although the presence of the noble metal Pd in this catalyst ex‐Co,Pd–La,Al‐HT (Co/Pd/La/Al=3/1/1/1) produces a similar catalytic activity to that of Rh‐containing catalyst, both in a N₂O‐containing stream and in one containing also SO₂ and O₂, but with a better performance in stability tests. PdO phase has been identified by XRD as being responsible for the considerable improvement in the activity. The presence of Mg as spinel structure exerts a stabilizing effect in the more active catalysts when mixtures of SO₂ and O₂ are considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Promotion of Ag/γ-Al2O3 by Cs for the SCR of NO by C3H6

The promotion of Ag/-Al₂O₃ by adding alkali metals (Li, Na, K, Cs) for selective catalytic reduction of NO with C₃H₆ was studied in this work. The activity of NO reduction was enhanced by addition of Cs to Ag/-Al₂O₃ in the presence of excess oxygen and SO₂. The stability and growth of silver oxide particles were promoted and the dispersion of silver particles on -Al₂O₃ was improved by the addition of 0.5 wt% Cs and 1 wt% Cs to 2 wt% Ag/-Al₂O₃, respectively. The results were confirmed by H₂ TPR, UV-Vis DRS, TEM, and XPS.     

Enhancement of Ca3Co4O9+δ thermoelectric properties by dispersing SiC nanoparticles

Misfit-layered oxides Ca₃Co₄O_9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) samples were synthesized using solid-state sintering method and the effects of SiC nanoparticles diapersion on the thermoelectric properties were investigated. Thermoelectric properties of Ca₃Co₄O_9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) were investigated up to 923 K. Compared with pure sample, the electrical resistivity of SiC-added samples reduces, for Ca₃Co₄O_9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) ceramic samples with x ≤ 0.05, the electrical resistivity decreases with increasing SiC nanoparticles adding amounts. And, the electrical resistivity exists transition from semiconductor to metal conduction mechanism. While, the thermal conductivity also decreases due to the addition of SiC nanoparticles. As a result, the Ca₃Co₄O_9+δ + 0.2 wt% SiC sample had the lowest thermal conductivity of 1.47 W/Km at 923 K, which was 18.4% lower than that of the Ca₃Co₄O_9+δ sample. The ZT value of Ca₃Co₄O_9+δ + 0.05 wt% SiC can reach 0.218, which is 40.9% higher than the pure Ca₃Co₄O_9+δ sample.     

Cobalt‐containing smectite‐like mesoporous material as a new type of catalyst for hydrodesulfurization of thiophene

Cobalt‐containing mesoporous smectite‐like material (SM(Co)) was prepared by a hydrothermal method and used as a catalyst for hydrodesulfurization (HDS) of thiophene. It is active by itself and produces mainly butenes and a small amount of n-butane. When platinum is added to this material, the HDS activity is enhanced by 50%, while the product distribution does not change so much. The platinum‐loaded sample should have two types of active sites, one originally present in the smectite‐like material and the other with platinum, the latter being different in nature from a sample of platinum supported on silica gel. Thus, the SM(Co) and Pt/SM(Co) samples are new types of HDS catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhancement in CO oxidation activity of nanosized CexZr1−xO2 solid solutions by incorporation of additional dopants

The influence of Hf, Pr and Tb dopant cations on structural and catalytic properties of nanosized Ce_xZr_1?xO₂ solid solutions has been investigated. A wide range of analytical techniques are utilized to characterize the synthesized materials, and the catalytic activity is evaluated for CO oxidation. XRD, Raman, SEM and TEM results suggested formation of dopant cation incorporated ceria–zirconia solid solutions with highly homogeneous morphology and lattice defects. The CO-TPR measurements revealed an enhanced reducibility of Ce_xZr_1?xO₂ which is reflected in their better catalytic activity. The role of Tb⁴⁺/Tb³⁺ and Pr⁴⁺/Pr³⁺ redox couples in facilitating a higher activity has been addressed.