Hierarchically porous monoliths of carbon and metal oxides with ordered mesopores

Grano, Amy J.; Sayler, Franchessa M.; Smått, Jan‐Henrik; Bakker, Martin G.

doi:10.1007/s10934-014-9861-0

Cited by 7 publications

(5 citation statements)

References 49 publications

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“…[124][125][126][127] Since their morphology can be widely tailored and monoliths created from silica or polymers easily disintegrated (e.g., by basic etching or hydrofluoric dissolution of silica; pyrolysis of polymers), they make ideal templates for the synthesis of monoliths with chemistries that are more suitable for other applications, such as carbon-based [128][129][130][131] or metal oxide structures. 132 The convenient control in combination with the versatility of morphologies that can be realized has stimulated numerous applications, including energy storage and conversion, 7,126,129,130,133,134 sensing, 129,135 separation, 117,119,136,137 and catalysis. 57,61,[138][139][140] 3.…”

Section: Monolithic Materialsmentioning

confidence: 99%

Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors

2016

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The targeted optimization of the functional properties of porous materials includes the understanding of their transport properties and thus requires knowledge about the relationship between material synthesis, resulting in three-dimensional material morphology, and relevant transport properties. In this Perspective, we present our views and results on the characterization of microscopic disorder in functional porous materials, which are widely used today as fixed beds in adsorption, separation, and catalysis. This allows us to identify structural parameters that impact their mass transport properties and eventually their overall performance in technological operations. We address this complex topic at the following levels: (i) computer-generation of disordered packings allows the systematic investigation of the bed porosity (packing density) and degree of packing heterogeneity. These studies are complemented by the physical reconstruction of real packed and monolithic beds, which resolves the salient features of the packing process and monolith synthesis that are under the control of the experimentalist. (ii) Once reconstructed packed-bed and monolith morphologies are available, they are analysed by statistical methods to derive structural descriptors for their mass transport properties. Spatial tessellation schemes and chord length distributions are shown to be suitable for that purpose. They lead us to sensitive correlations of the degree of pore-environment heterogeneity and packing-scale disorder with the dynamics of (random) diffusion and (flow-field dependent) hydrodynamic dispersion, respectively. (iii) Direct or pore-scale numerical simulations are implemented on a highperformance computing platform to quantify the relevant transport properties of the materials. This complementary approach highlights the morphological descriptors of mass transport efficiency. They are validated by the simulations and in the future could direct the rational design of materials from their synthesis to targeted applications based on physical reconstruction.

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Section: Monolithic Materialsmentioning

confidence: 99%

Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors

2016

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“…Monolithic reactors may surpass most drawbacks typical of packed-bed systems, including high pressure drops, low contacting efficiency, large distribution of residence times, formation of hot-spots or stagnation zones, which results in poorly controlled fluid dynamics, hence in low catalyst productivity and selectivity [ 105 – 106 ]. Particularly, monoliths featuring a 3D isotropic, hierarchically porous network of narrowly size distributed, interconnected macropores (1–30 μm) and mesopores within the struts (6–50 nm) have shown a unique hydrodynamic behavior in the liquid phase [ 107 – 108 ], which addresses the need of both efficient processing (within small pores) and effective mass transport (by macropores) [ 109 – 110 ]. This kind of monolith obtained by spinodal decomposition joins the advantages of high surface area typical of mesoporous material, spanning from 200 to 1200 m 2 g −1 [ 111 ] with a high permeability typical of macropores, which results in a very efficient mass transfer [ 112 ].…”

Section: Reviewmentioning

confidence: 99%

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

Moreno‐Marrodán

Liguori

Barbaro

2017

Beilstein J. Org. Chem.

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The catalytic partial hydrogenation of substituted alkynes to alkenes is a process of high importance in the manufacture of several market chemicals. The present paper shortly reviews the heterogeneous catalytic systems engineered for this reaction under continuous flow and in the liquid phase. The main contributions appeared in the literature from 1997 up to August 2016 are discussed in terms of reactor design. A comparison with batch and industrial processes is provided whenever possible. 734

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“…[34] Despite their advantages, use of hierarchically porous inorganic monoliths in flow catalysis hasb een scarcely investigated so far,b eing essentially exploredf or HPLC applications. [53] Solid acid catalysis is of paramount importance in both the hydrocarbon [54,55] and the biorefinery industry,w herein conversion of real feedstocks( e.g.,a queous solutions of carbohydrates), [56,57] usually requires tolerance to water and to medium to high temperatures. [39] Specific functionalization of the monolithic material may also be required for catalytic applications.…”

Section: Introductionmentioning

confidence: 99%

“…[46,50] All above findings show the advantages of unconventional inorganic monolithic catalysts compared with the classical heterogeneous ones. [53] Solid acid catalysis is of paramount importance in both the hydrocarbon [54,55] and the biorefinery industry,w herein conversion of real feedstocks( e.g.,a queous solutions of carbohydrates), [56,57] usually requires tolerance to water and to medium to high temperatures. [58] Prompted by the low efficiency and the unsatisfactory thermals tability of the previously reported monolithic acid catalysts (i.e.,z irconium phosphate [45] and sulfonateds ilica [59] ), we sought to develop alternative materials with improved performance for the conversion of biomass-derived substrates under continuous-flow conditions.…”

Section: Introductionmentioning

confidence: 99%

Low‐Temperature Continuous‐Flow Dehydration of Xylose Over Water‐Tolerant Niobia–Titania Heterogeneous Catalysts

et al. 2018

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The sustainable conversion of vegetable biomass-derived feeds to useful chemicals requires innovative routes meeting environmental and economical criteria. The approach herein pursued is the synthesis of water-tolerant, unconventional solid acid monolithic catalysts based on a mixed niobia-titania skeleton building up a hierarchical open-cell network of meso- and macropores, and tailored for use under continuous-flow conditions. The materials were characterized by spectroscopic, microscopy, and diffraction techniques, showing a reproducible isotropic structure and an increasing Lewis/Brønsted acid sites ratio with increasing Nb content. The catalytic dehydration reaction of xylose to furfural was investigated as a representative application. The efficiency of the catalyst was found to be dramatically affected by the niobia content in the titania lattice. The presence of as low as 2 wt % niobium resulted in the highest furfural yield at 140 °C under continuous-flow conditions, by using H O/γ-valerolactone as a safe monophasic solvent system. The interception of a transient 2,5-anhydroxylose species suggested the dehydration process occurs via a cyclic intermediates mechanism. The catalytic activity and the formation of the anhydro intermediate were related to the Lewis acid sites (LAS)/Brønsted acid sites (BAS) ratio and indicated a significant contribution of xylose-xylulose isomerization. No significant catalyst deactivation was observed over 4 days usage.

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Hierarchically porous monoliths of carbon and metal oxides with ordered mesopores

Cited by 7 publications

References 49 publications

Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors

Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

Low‐Temperature Continuous‐Flow Dehydration of Xylose Over Water‐Tolerant Niobia–Titania Heterogeneous Catalysts

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