Deactivation Of Catalytic Activity Research Articles

Investigating the Texture and Antioxidant Capacity of Papain and Trans-glutaminase Enzyme-treated Yogurt with Different Carbohydrates – Glucose, Sucrose and Maltodextrin

Yogurt is considered as a functional food, which is a complex mixture of different biological components. Functional foods are designed to have physio-logical benefits and reduce the risk of chronic diseases beyond basic nutritional functions, and may be similar in appearance of conventional food. Therefore, the consumption of dairy products is highly recommended. In this study, the average composition milk was purchased in a local supermarket. Subsequently, ultrafiltration of milk was carried out with a tubular membrane, placed in a laboratory-developed cross-flow membrane module. Pore size and active surface area of tubular membrane were 5 nm and 0.005 m2, respectively. A static turbulence promoter was placed inside of membrane tube. Retentate of ultrafiltration membrane was treated with different concentrations of papain at temperature 50 °C for 10 minutes and subsequently, deactivation of enzymatic activity was performed at temperature 70 °C for 20 minutes. After deactivation of catalytic activity of papain, milks were fermented with yogurt starter culture (Thermophilic YoFlex® culture) at temperature 45 °C for 6 hours. During fermentation, transglutaminase and different types of carbohydrates, such as glucose, maltodextrin and sucrose were introduced with the aid of changing texture and antioxidant capacity of yogurt. Antioxidant capacity and hardness of yogurt, prepared with cow's milk were 0.44 mmol eqv. ascorbic acid/L and 0.58 Newton, respectively. It was found that application of enzyme (both papain and transglutaminase) and maltodextrin increased the antioxidant capacity of yogurt. Furthermore, it was found that hardness of yogurt was increased by addition of carbohydrate.

Support interaction of Pt/CeO2 and Pt/SiC catalysts prepared by nano platinum colloid deposition for CO oxidation

The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance. Herein, Pt/CeO2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method, and their catalytic performance in CO oxidation was investigated. XRD, TEM, XPS and H2-TPR were used to identify the states of Pt particles on the support surface, as well as their effect on the performance of the catalysts. Formation of the Pt–O–Ce interaction is one of the factors controlling catalyst activity. Under the oxidative treatment at low temperature, the Pt–O–Ce interaction plays an important role in improving the catalytic activity. After calcining at high temperature, enhanced Pt–O–Ce interaction results in the absence of metallic Pt0 on the support surface, as evidenced by the appearance of Pt2+ species. It is consistent with the XPS data of Pt/CeO2, and is the main reason behind the deactivation of the catalyst. By contrast, either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt0 state on the SiC surface even after aging at 800 °C in an oxidizing atmosphere. Thus, the Pt/SiC shows better thermal stability than Pt/CeO2. The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature, but strong interactions may induce serious deactivation of catalytic activity.

Transesterification of propylene glycol methyl ether by reactive simulated moving bed chromatography using homogeneous catalyst

A reactive chromatography process was investigated for a transesterification reaction of propylene glycol methyl ether (DOWANOL™ PM) using a homogeneous catalyst, a sodium alkoxide. In the proposed process, fresh catalyst is supplied with desorbent, which allows independent optimization of the adsorption properties of the stationary phase. Deactivation of catalytic activity can be avoided, which had been found to be the bottleneck in our previous study for heterogeneous catalysis. To model and optimize this process, a series of batch reaction experiments, and pulse injection tests with a chromatographic column with and without reaction were carried out. From the experimental data, equilibrium and kinetic parameters were estimated using the inverse method. Using this model, a simulated moving bed reactor was designed that achieves a conversion of 95% using the homogeneous catalysis concept.

Synthesis and Application of Hyperbranched Polyester-Grafted Polyethylene (HBPE-g-PE) Containing Palladium Nanoparticles as Efficient Nanocatalyst

In nowadays, palladium-catalyzed reactions are of utmost importance in synthetic organic chemistry. Due to advantages of heterogeneous catalysts such as the easy handling and good recyclability, usually these types of catalysts are first choice in constructing a new catalytic system. Here we report a facile approach to prepare hyperbranched polyester-grafted-polyethylene supported palladium nanoparticles as an efficient catalyst in Suzuki reaction and solvent-free aerobic oxidation of alcohols. The reactions were carried out in different conditions with various reagents and the efficiency was determined. Because of the amplification effect of hyperbranched polyester, high loading capacities (around 0.276 mmol g−1 for Pd) was achieved. The catalyst was characterized with X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis. This metal nanocatalyst has a very low leaching loss, high activity and selectivity, excellent thermal stability and can be reused at least five times without deactivation of catalytic activity. In this work, a hyperbranched polyester based on 2,2-bis (methylol) propionic acid (bis-MPA) was synthesized and grafted onto carboxylic acid functionalized polyethylene powder. The final nanocatalyst was prepared via solution loading of PdCl2 and reduction to palladium nanoparticles on the HBPE-g-PE. The activity and stability of prepared polymer-supported heterogeneous catalyst was carefully examined for Suzuki reaction and solvent-free oxidation of alcohols.

Alumina-supported CuO–CeO2–ZrO2 Catalysts for CO Oxidation – Preparation and Characterization

The effect of catalyst samples, prepared by different methods, having the composition (CuCe5.17Zr3.83Ox/γ-Al2O3 (20 wt%) was studied in the present work for carbon monoxide (CO) oxidation. Cu(NO3)23H2O was used as a precursor for the preparation of the catalysts. Catalysts were prepared by four methods: co-impregnation, citric acid sol–gel, urea nitrate combustion and urea gelation co-precipitation methods. Prepared catalysts were characterized by BET specific surface area, X-ray diffraction, thermogravimetic analysis/differential scanning calorimetry (TGA/DSC) and scanning electron microscopy (SEM) techniques. The oxidation of CO was carried out in a tubular fixed bed reactor at atmospheric pressure and at temperature ranging from ambient to 250°C. A fixed weight (100 mg) of the catalyst was taken and 2.5% CO in air at a total feed rate of 60 ml/min was used in the reactor. It was observed that the performance of the catalysts in CO oxidation was influenced by the preparation methods. The catalyst prepared by sol–gel method that calcined at 500°C exhibited excellent activity for CO oxidation with total conversion at 210°C. The ranking order of the alumina supporting CuO–CeO2–ZrO2 catalysts was as follows: sol–gel > co-impregnation > urea gelation > urea nitrate combustion. The four catalysts prepared did not show deactivation of catalytic activity for 50 h of continuous runs.

Viral templated palladium nanocatalysts for dichromate reduction

Despite recent progress on environmental catalysis, there exist several critical challenges in simple and readily controllable nanocatalyst synthesis including the unpredictable particle growth, deactivation of catalytic activity, cumbersome catalyst recovery and lack of in situ reaction monitoring. We demonstrate viral template-based bottom-up assembly approach for nanostructured palladium (Pd) catalyst synthesis for dichromate reduction. Specifically, genetically displayed cysteine residues on each coat protein of Tobacco Mosaic Virus (TMV) templates provide precisely spaced thiol functionalities for readily controllable surface assembly and catalytically active Pd nanoparticle formation. Reaction kinetics studies via in situ monitoring by UV–vis spectroscopy revealed catalytic activity, stability and first-order batch reaction kinetics, and allowed rapid examination of reaction parameters (pH, reducer and temperature). Further, in-depth characterization via AFM, GISAXS and XPS show preferential Pd nanoparticle formation on TMV templates, particle size and stability that correlate well with the reaction kinetics results. We envision that our approach for simple high density surface assembly of catalytically active Pd nanoparticles under mild aqueous conditions would provide a facile route to catalyst synthesis in a wide range of applications.

Effect of mileage on the deactivation of vehicle-aged three-way catalysts

Two used three-way catalysts (TWC) removed from the same type of automobiles but with different mileages were characterised (by XRD, TPR, N 2 adsorption and TXRF) and their catalytic properties were tested. Both used catalysts were clearly deactivated, especially as regards the elimination of NO and propylene. CO oxidation was much less affected. The data on activity suggest that the rate of deactivation slows down beyond a certain mileage. Attention was focused on the changes brought about by mileage in the textural properties, the deposition of contaminants (mainly P, Zn and Pb), the alteration of the reducibility of Ce oxide and the formation of phases between contaminants and washcoat components (CePO 4 and Zn 2P 2O 7). The results were compared with those from a fresh counterpart catalyst. The dependence of all the above effects on mileage and the impact on the deactivation of catalytic activity is discussed critically. It is suggested that although other effects may play a secondary role in the used TWC catalysts studied in this work Pb poisoning exerts a definitive impact on the deactivation of the catalytic activity.

Oxidative Dehydrogenation of Ethane over Alkali Metal Chloride Modified Silica Catalysts

The catalytic oxidative dehydrogenation of ethane into ethylene was investigated over a series of alkali metal chloride supported on silica catalysts. It is found that alkali metal chloride modified silica catalysts show much higher activity in the selective oxidation of ethane than silica support itself, and their catalytic activity depends on the nature of alkali metal and its loading. LiCl/SiO2 exhibits the highest ethane conversion and ethylene yield, giving 99% ethane conversion and 80% ethylene selectivity at 600 °C. However, it shows rapid deactivation. NaCl/SiO2 shows high conversion and a longer stability. On the contrary, KCl/SiO2 displays the lowest ethane conversion but a high deactivation rate. Characterization of the catalysts reveals that the activity variation can be related to the redox and acid−base properties of the catalysts. The deactivation of catalytic activity can be attributed to the loss of chlorine and chemical phase transformation.