Catalysts

3046 KiB

Open AccessArticle

Valorisation of Vietnamese Rice Straw Waste: Catalytic Aqueous Phase Reforming of Hydrolysate from Steam Explosion to Platform Chemicals

by Cao Huong Giang, Amin Osatiashtiani, Vannia Cristina Dos Santos, Adam F. Lee, David R. Wilson, Keith W. Waldron and Karen Wilson

Catalysts 2014, 4(4), 414-426; https://doi.org/10.3390/catal4040414 - 15 Dec 2014

Cited by 15 | Viewed by 6765

Abstract

A family of tungstated zirconia solid acid catalysts were synthesised via wet impregnation and subsequent thermochemical processing for the transformation of glucose to 5-hydroxymethylfurfural (HMF). Acid strength increased with tungsten loading and calcination temperature, associated with stabilisation of tetragonal zirconia. High tungsten dispersions of between 2 and 7 W atoms·nm⁻² were obtained in all cases, equating to sub-monolayer coverages. Glucose isomerisation and subsequent dehydration via fructose to HMF increased with W loading and calcination temperature up to 600 °C, indicating that glucose conversion to fructose was favoured over weak Lewis acid and/or base sites associated with the zirconia support, while fructose dehydration and HMF formation was favoured over Brönsted acidic WO_x clusters. Aqueous phase reforming of steam exploded rice straw hydrolysate and condensate was explored heterogeneously for the first time over a 10 wt% WZ catalyst, resulting in excellent HMF yields as high as 15% under mild reaction conditions. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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10693 KiB

Open AccessArticle

Catalytic Glycerol Hydrodeoxygenation under Inert Atmosphere: Ethanol as a Hydrogen Donor

by Efterpi S. Vasiliadou and Angeliki A. Lemonidou

Catalysts 2014, 4(4), 397-413; https://doi.org/10.3390/catal4040397 - 15 Dec 2014

Cited by 16 | Viewed by 6784

Abstract

Glycerol hydrodeoxygenation to 1,2-propanediol (1,2-PDO) is a reaction of high interest. However, the need for hydrogen supply is a main drawback of the process. According to the concept investigated here, 1,2-propanediol is efficiently formed using bio-glycerol feedstock with H₂ formed in situ via ethanol aqueous phase reforming. Ethanol is thought to be a promising H₂ source, as it is alcohol that can be used instead of methanol for transesterification of oils and fats. The H₂ generated is consumed in the tandem reaction of glycerol hydrodeoxygenation. The reaction cycle proceeds in liquid phase at 220–250 °C and 1.5–3.5 MPa initial N₂ pressure for a 2 and 4-h reaction time. Pt-, Ni- and Cu-based catalysts have been synthesized, characterized and evaluated in the reaction. Among the materials tested, Pt/Fe₂O₃-Al₂O₃ exhibited the most promising performance in terms of 1,2-propanediol productivity, while reusability tests showed a stable behavior. Structural integrity and no formation of carbonaceous deposits were verified via Temperature Programmed Desorption of hydrogen (TPD-H₂) and thermogravimetric analysis of the fresh and used Pt/FeAl catalyst. A study on the effect of various operating conditions (reaction time, temperature and pressure) indicated that in order to maximize 1,2-propanediol productivity and yield, milder reaction conditions should be applied. The highest 1,2-propanediol yield, 53% (1.1 g_1,2-PDO g_cat⁻¹·h⁻¹), was achieved at a lower reaction temperature of 220 °C. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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4007 KiB

Open AccessArticle

How to Determine the Core-Shell Nature in Bimetallic Catalyst Particles?

by Emma Westsson and Ger J.M. Koper

Catalysts 2014, 4(4), 375-396; https://doi.org/10.3390/catal4040375 - 28 Nov 2014

Cited by 29 | Viewed by 8575

Abstract

Nanometer-sized materials have significantly different chemical and physical properties compared to bulk material. However, these properties do not only depend on the elemental composition but also on the structure, shape, size and arrangement. Hence, it is not only of great importance to develop synthesis routes that enable control over the final structure but also characterization strategies that verify the exact nature of the nanoparticles obtained. Here, we consider the verification of contemporary synthesis strategies for the preparation of bimetallic core-shell particles in particular in relation to potential particle structures, such as partial absence of core, alloying and raspberry-like surface. It is discussed what properties must be investigated in order to fully confirm a covering, pin-hole free shell and which characterization techniques can provide such information. Not uncommonly, characterization strategies of core-shell particles rely heavily on visual imaging like transmission electron microscopy. The strengths and weaknesses of various techniques based on scattering, diffraction, transmission and absorption for investigating core-shell particles are discussed and, in particular, cases where structural ambiguities still remain will be highlighted. Our main conclusion is that for particles with extremely thin or mono-layered shells—i.e., structures outside the limitation of most imaging techniques—other strategies, not involving spectroscopy or imaging, are to be employed. We will provide a specific example of Fe-Pt core-shell particles prepared in bicontinuous microemulsion and point out the difficulties that arise in the characterization process of such particles. Full article

(This article belongs to the Special Issue Synthesis of Nanostructured Catalytic Materials from Microemulsions)

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6592 KiB

Open AccessReview

Metallic Clusters: Theoretical Background, Properties and Synthesis in Microemulsions

by David Buceta, Yolanda Piñeiro, Carlos Vázquez-Vázquez, José Rivas and Manuel Arturo López-Quintela

Catalysts 2014, 4(4), 356-374; https://doi.org/10.3390/catal4040356 - 03 Nov 2014

Cited by 51 | Viewed by 8944

Abstract

Reducing the size from the bulk material to nanoparticles produces a scaling behavior in physical properties in the later ones, due to the large surface-to-volume fraction. By further size reduction, entering into the subnanometric cluster region, physical properties are largely affected by strong quantum confinement. These quantum size effects (HOMO-LUMO gap), the small size and the specific geometry award subnanometric clusters with totally new and fascinating properties, including cluster photoluminescence, enhanced catalytic activity, etc. In this review, we report an introduction to the physical properties of clusters based on the jellium model; the controlled synthesis by microemulsion methods and the catalytic properties in different areas as heterogeneous catalysis, photocatalysis or electrocatalysis among others. Full article

(This article belongs to the Special Issue Synthesis of Nanostructured Catalytic Materials from Microemulsions)

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3936 KiB

Open AccessArticle

Synthesis and Evaluation of Porous Semiconductor Hexaniobate Nanotubes for Photolysis of Organic Dyes in Wastewater

by Maryam Zarei-Chaleshtori, Victor Correa, Natalie López, Manuel Ramos, Roya Edalatpour, Nancy Rondeau and Russell R. Chianelli

Catalysts 2014, 4(4), 346-355; https://doi.org/10.3390/catal4040346 - 27 Oct 2014

Cited by 13 | Viewed by 5508

Abstract

We present the chemical synthesis of hexaniobate nanotubes using two routes, (1) starting material K₄Nb₆O₁₇ and (2) parent material of H₄Nb₆O₁₇ via ion exchange. The as-synthesized materials were exfoliated by adjusting the pH to 9–10 using tetra-n-butylammonioum hydroxide (TBA⁺OH⁻), leading to a formation of hexaniobate nanotubes. In order to understand morphology a full characterization was conducted using SEM, HRTEM, BET and powder-XRD. The photocatalytic activity was evaluated using photolysis method using Bromocresol Green (BG) and Methyl Orange (MO) as model contaminants. Results indicate a nanotube porous oxide with large porous and surface area; the photocatalytic activity is about 95% efficient when comparing with commercial TiO₂. Full article

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Catalysts, Volume 4, Issue 4 (December 2014) – 5 articles , Pages 346-426

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