Dry re-forming of methane with CO2 was investigated over bimetallic W and Ni incorporated mesoporous alumina catalysts prepared by the one-pot sol–gel route. Powdered materials were thoroughly ...characterized (N2 physisorption, XRD, XPS, SEM-EDX, TGA-DTA, TPH) prior to and after catalytic runs performed at 600 and 750 °C. High surface area W–Ni incorporated mesoporous alumina catalysts (S BET = 178–192 m2/g) synthesized in this work showed excellent performance for the conversion of model biogas to synthesis gas. The Ni–W containing materials exhibited high catalytic activity, which was maintained throughout 150 h of time-on-stream (TOS) long-term operation at 750 °C. Increase of the W loading (0–10–15 wt %) at fixed nickel amount (5 wt %) resulted in prevented deactivation of the catalyst, most prominent at 600 °C, and minimization of coke formation on the surface of the catalyst. Tungsten incorporation was thus proven to significantly enhance and stabilize the overall catalyst performance.
To attain sustained activity and stability in CH4–CO2 dry reforming (CCDR), two nanocomposite materials comprising silicon carbide or alumina and ceria–zirconia were introduced to support ...cobalt–nickel (CoNi) catalysts. Following the sequential impregnation-ultrasonication–deposition precipitation procedure, catalysts were systematically characterized and their performances were tested at 1.2 bar and 750 °C, where undiluted CH4–CO2 (ratio = 1:1) streams simulating biogas and the real industrial conditions were fed into a continuous flow reactor. For CCDR reactions conducted at a weight hourly space velocity (WHSV) of 12 L/(gcat h), good activity and stability were shown for both catalysts. Carbon content as low as 0.3 wt % and high conversions (70%–78% and 78%–88% for CH4 and CO2, respectively) were recorded over 23 h and 550 h tests. Interestingly, by increasing the WHSV value to an order of magnitude higher, i.e., at 120 L/(gcat h) with all other conditions held constant, a 6 h short-term test showed remarkably high conversions near equilibrium values, implying that the reactions still occurred within the thermodynamic regime, despite a reduced 10-fold mass of catalyst bed. This infers that not all active sites available on the catalyst surface were fully exploited. Compared to previous catalyst performances, the progress made in this work is ascribed to the synergistic effects from selected support materials that contributed remarkable redox properties, high surface area, mechanical and thermal stability to the catalysts.
We investigated the influence of archaeal lipids (C25,25) isolated from thermophilic archaeon Aeropyrum pernix K1 on physicochemical properties of liposomes comprised of egg sphingomyelin (SM) and ...cholesterol (CH) using fluorescence emission anisotropy, calcein release studies, dynamic light scattering, transmission electron microscopy and phase analysis light scattering. The 2 mol% addition of archaeal lipids enabled formation of small unilamellar vesicles by sonication while also having significant effect on reducing mean size, polydispersity index and zeta potential of C25,25/SM/CH vesicles. Increasing the ratio of C25,25 lipids in mixture of C25,25/SM/CH decreased lipid ordering parameter in dose dependent manner at different temperatures. We also demonstrated that adding 15 mol% C25,25 to SM/CH mixture will cause it to notably interact with fetal bovine serum which could make them a viable alternative adjuvant to synthetic ether-linked lipids in development of advanced liposomal vaccine delivery systems. The prospect of combining the proven strengths of SM/CH mixtures with the unique properties of C25,25 opens exciting possibilities for advancing drug delivery technologies, promising to yield formulations that are both highly effective and adaptable to a range of therapeutic applications.
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•Archaeal lipids in SM-CH liposomes enable formation of vesicles by sonication.•Archaeal lipids increase fluidity in SM-CH liposomes dose-dependently.•2 mol% addition of archaeal lipids stabilizes the SM-CH liposomes.•Mixed liposomes show morphological stability and reduced calcein release.
Adverse environmental conditions are severely limiting the use of microorganisms in food systems, such as probiotic delivery, where low pH causes a rapid decrease in the survival of ingested ...bacteria, and mixed-culture fermentation, where stepwise changes and/or metabolites of individual microbial groups can hinder overall growth and production. In our study, model probiotic lactic acid bacteria (
ATCC 8014,
GG) and yeasts native to dairy mixed cultures (
ZIM 1868) were entrapped in an optimized (cell, alginate and hardening solution concentration, electrostatic working parameters) Ca-alginate system. Encapsulated cultures were examined for short-term survival in the absence of nutrients (lactic acid bacteria) and long-term performance in acidified conditions (yeasts). In particular, the use of encapsulated yeasts in these conditions has not been previously examined. Electrostatic manufacturing allowed for the preparation of well-defined alginate microbeads (180-260 µm diameter), high cell-entrapment (95%) and viability (90%), and uniform distribution of the encapsulated cells throughout the hydrogel matrix. The entrapped
maintained improved viabilities during 180 min at pH 2.0 (19% higher when compared to the free culture), whereas,
appeared to be less robust. The encapsulated
exhibited double product yields in lactose- and lactic acid-modified MRS growth media (compared to an unfavorable growth environment for freely suspended cells). Even within a conventional encapsulation system, the pH responsive features of alginate provided superior protection and production of encapsulated yeasts, allowing several applications in lacto-fermented or acidified growth environments, further options for process optimization, and novel carrier design strategies based on inhibitor charge expulsion.
Capsulation of non-dewaxed propolis in gum Arabic via freeze-drying maintains higher bioflavonoid content in comparison to spray-drying. Encapsulated propolis also prolongs fish oil shelf life.
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•Gum Arabic encapsulates non-dewaxed propolis better than inulin or maltodextrin.•Freeze-drying is more efficient in encapsulating propolis than spray-drying.•Encapsulated propolis powders prolong shelf life of oil rich in omega-3 fatty acids.•Omission of dewaxing is reflected in higher phenol levels and better stability.•Different analysis confirm successful encapsulation of propolis with gum Arabic.
The aim was to obtain alcohol-free, water-dispersible propolis powder from non-dewaxed propolis extract, with high levels of phenols, with either freeze-drying or spray-drying. Optimisation was performed with different wall materials, centrifugation settings and propolis:carrier ratios, and was carried out by monitoring the effect of one parameter at a time on the dependable variables. The powders obtained contained high phenol levels, which included known bioactive components, and also showed high dispersibility in cold water and high antioxidant activity. Furthermore, the propolis powders were stable in water for up to 24h, and the release of encapsulated phenols did not change across different environmental values, as pH 3–6. Differential scanning calorimetry showed that propolis interacts with and stabilises the carrier material (gum Arabic), also high pressure liquid chromatography showed that the profiles of the powders remained unchanged across all encapsulation techniques. This study demonstrates that the same propolis formulations can be fine-tuned to suit specific final applications and confirms that freeze-drying is a viable alternative to the more established spray-drying for encapsulation of propolis. This study also demonstrates that non-dewaxed propolis extract is a better alternative for encapsulation purposes, as no phenolic compounds are lost during its processing.
Propolis is a resinous compound made by bees with well-known biological activity. However, comparisons between encapsulated and non-encapsulated propolis are lacking. Therefore, the antibacterial ...activity, effect on the phase transition of lipids, and inhibition of UV-induced lipid oxidation of the two forms of propolis were compared. The results showed that non-encapsulated propolis produces quicker effects, thus being better suited when more immediate effects are required (e.g., antibacterial activity). In order to gain an in-depth introspective on these effects, we further studied the synergistic effect of propolis compounds on the integrity of lipid membranes. The knowledge of component synergism is important for the understanding of effective propolis pathways and for the perspective of modes of action of synergism between different polyphenols in various extracts. Thus, five representative molecules, all previously isolated from propolis (chrysin, quercetin,
-ferulic acid, caffeic acid, (-)-epigallocatechin-3-gallate) were mixed, and their synergistic effects on lipid bilayers were investigated, mainly using DSC. The results showed that some compounds (quercetin, chrysin) exhibit synergism, whereas others (caffeic acid,
-ferulic acid) do not show any such effects. The results also showed that the synergistic effects of mixtures composed from several different compounds are extremely complex to study, and that their prediction requires further modeling approaches.
The encapsulation of proteins into core-shell structures is a widely utilised strategy for controlling protein stability, delivery and release. Despite the recognised utility of these ...microstructures, however, core-shell fabrication routes are often too costly or poorly scalable to allow for industrial translation. Furthermore, many scalable routes rely upon emulsion-techniques implicating denaturing or environmentally harmful organic solvents. Herein, we investigate core-shell protein encapsulation through single-feed, aqueous spray drying: a cheap, industrially ubiquitous particle-formation technology in the absence of organic solvents. We show that an excipient's preference for the surface of the spray dried particle is well-predicted by its hydrodynamic diameter (Dh) under relevant feed buffer conditions (pH and ionic strength) and that the predictive power of Dh is improved when measured at the spray dryer outlet temperature compared to room temperature (R2 = 0.64 vs. 0.59). Lastly, we leverage these findings to propose an adaptable design framework for fabricating core-shell protein encapsulates by single-feed aqueous spray drying.
•High OSC of CeZrO2 solid solution provides the functionality to oxidize formed coke.•Marginal improvement in catalytic activity is obtained with excessive NiCo loading.•No coke had accumulated after ...400h TOS at 1023K and equimolar CH4/CO2 feed.•CH4/CO2 feed ratio higher that 1 drastically accelerates coke accumulation.
This study investigates how morphology, active metal content and oxygen storage capacity of various bimetallic NiCo/CeZrO2 materials influence their catalytic activity and stability in the methane dry reforming reaction. Catalyst preparation procedure and chemical composition were steered to finally obtain materials, which do not accumulate carbon during the CH4/CO2 reforming reaction. Oxygen storage capacity of the CeZrO2 catalyst support was identified to play a vital role in retarding carbon accumulation over the tested NiCo/CeZrO2 materials. This property can be fully developed when a nanocrystalline solid solution of CeO2 and ZrO2 is formed. Secondly, a high dispersion of nickel and cobalt is crucial for two reasons: (i) catalysts which contain larger NiCo bimetallic particles (for example with 12–18wt.% active metal loading) exhibit a low metal-support interphase that results in enhanced coke formation rates; (ii) additionally, only a marginal gain in methane reforming rates are achieved at higher loadings, compared to catalysts with a 3–6wt.% active metal content. We demonstrated that a NiCo/CeZrO2 catalyst under relevant operating conditions after 400h TOS maintains 79 and 84% conversion of CH4 and CO2, with negligible coke accumulation.
To improve the activity of nickel–cobalt (NiCo) catalyst supported on ceria-zirconia (CeZr) in the dry reforming of methane (DRM) with carbon dioxide, and to lower the coking rate in this process, ...1.5 wt.% and 2.5 wt.% NiCo catalysts were prepared using two approaches, i.e. freeze-drying (FD) and NO calcination for comparison against oven-drying (OD) and air calcination (air), respectively. Their impact was studied for 20 h of DRM at 750 °C and 1.2 bar, with undiluted CH4–CO2 feed simulating the real conditions. NO-calcined samples show, on average, more pronounced improvement through increased conversion of CH4 (90%), followed by FD samples (85%) from the air and OD-prepared samples (both 82%). Coking content varied between 0.67 and 0.82 wt.%. The observed slow catalyst deactivation might be caused by sintering of the catalysts. Higher quantity of CO than H2 for syngas production was obtained, owing to concurrent reverse water-gas shift side reaction, and high redox properties of the defective CeZr lattice that enabled surface carbon gasification by continuous replenishment of oxygen from the support to produce CO, of which the latter phenomenon also explains the low carbon deposition. H2/CO ratio between 0.42 and 0.85 was achieved, with FD and NO samples fared better (0.83–0.85) over the ones prepared by conventional methods (0.73–0.82) for 2.5%NiCo loaded catalysts.
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•CH4–CO2 conversion for NO and FD catalyst is higher than air and OD-prepared ones.•Selectivity of syngas is high (averaging at 75–85%) for the former catalysts.•Higher metal loading (2.5 > 1.5 wt.% NiCo) can better depress RWGS side reaction.•Low coking content (0.67–0.82 wt.%) were obtained for 20 h of dry reforming tests.
Encapsulation provides efficient approaches to increase stability and delivery of poorly soluble bioactive components, predominantly for fortification of beverages and similar liquid-based foods. In ...this study, folic acid was encapsulated within conventional and emulsion-templated alginate-pectin hydrogels, proliposomes, and a combination thereof. The stability of these systems was examined under various environmental conditions (pH 1.2-9.0, 25-85 °C, dark/light). The techniques demonstrated efficient and relatively straightforward production of well-defined microparticles and nanoparticles (350 nm to 250 μm). Dispersed folic acid provided a delivery system with unique pH-responsive features, which offered prolonged stability during food storage, and indicated increased release at the site of absorption upon ingestion. This formulation had no limitation due to particle size, while at the same time it allowed high encapsulation efficiencies (80%-100%), as compared to the low encapsulation efficiency achieved by solubilisation (6%). At the low pH that is expected in the stomach, leaching of the dispersed folic acid was prevented, while at the pH that is expected in the intestine, there was complete release via solubilisation and carrier swelling. Overall, the optimum for food processing and storage was pH 3.0, where ≥70% of 50% to 200% of the recommended daily allowance of folic acid remained in the alginate-pectin beads after 6 months at room temperature in the dark. The thermal properties were enhanced by emulsion-templated alginate-pectin beads and proliposomes. In this way, 30% to 75% retention of folic acid was achieved at temperatures ≤90 °C, where the proliposomes reinforced within a polysaccharide network achieved the highest level of protection.
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