3D printing of materials with active functional groups can provide custom-designed structures that promote chemical conversions. Herein, catalytically active architectures were produced by photopolymerizing bifunctional molecules using a commercial stereolithographic 3D printer. Functionalities in the monomers included a polymerizable vinyl group to assemble the 3D structures and a secondary group to provide them with active sites. The 3D-printed architectures containing accessible carboxylic acid, amine, and copper carboxylate functionalities were catalytically active for the Mannich, aldol, and Huisgen cycloaddition reactions, respectively. The functional groups in the 3D-printed structures were also amenable to postprinting chemical modification. As proof of principle, chemically active cuvette adaptors were 3D printed and used to measure in situ the kinetics of a heterogeneously catalyzed Mannich reaction in a conventional solution spectrophotometer. In addition, 3D-printed millifluidic devices with catalytically active copper carboxylate complexes were used to promote azide–alkyne cycloaddition under flow conditions. The importance of controlling the 3D architecture of the millifluidic devices was evidenced by enhancing reaction conversion upon increasing the complexity of the 3D prints.Keywords: 3D printing; additive manufacturing; catalysis; millifluidics; polymeric materials;

Deposition of trimethylphosphate onto ceria followed by thermal treatment resulted in the formation of surface phosphates with retention of the ceria fluorite structure. The structural and chemical properties of the phosphate-functionalized ceria were studied using 31P solid-state NMR, XPS, zeta titration, ammonia thermal desorption, pyridine adsorption, and model reactions. The introduction of phosphates generated Brønsted acid sites and decreased the number of Lewis acid sites on the surface. The relative amount of Lewis and Brønsted acids can be controlled by the amount of trimethylphosphate used in the synthesis. Upon deposition of Pd, the multifunctional material showed enhanced activity for the hydrogenolysis of eugenol and guaiacol compared to Pd on the unmodified ceria support. This was attributed to the cooperativity between the Lewis acid sites, which activate the substrate for dearomatization, and the redox/Brønsted acid properties, which catalyze hydrogenolysis.

The stability of palladium supported on ceria (Pd/CeO2) was studied during liquid flow transfer hydrogenation using primary and secondary alcohols as hydrogen donors. For primary alcohols, the ceria support was reduced to cerium hydroxy carbonate within 14 h and was a contributing factor toward catalyst deactivation. For secondary alcohols, cerium hydroxy carbonate was not observed during the same time period and the catalyst was stable upon prolonged reaction. Regeneration through oxidation/reduction does not restore initial activity likely due to irreversible catalyst restructuring. A deactivation mechanism involving C–C scission of acyl and carboxylate intermediates is proposed.

The selective hydrogenation of fatty acids to fatty alcohols can be achieved under moderate conditions (180 °C, 30 bar H2) by simultaneously supporting copper and iron oxides on mesoporous silica nanoparticles. The activity of the cosupported oxides is significantly higher than that of each supported metal oxide and of a physical mixture of both individually supported metal oxides. A strong interaction between both metal oxides is evident from dispersion, XRD, TPR, and acetic acid TPD measurements, which is likely responsible for the synergistic behavior of the catalyst. Copper oxide is reduced in situ to its metallic form and thereby activates hydrogen. It is proposed that hydrogen spills over to iron oxide where fatty acids bind and are selectively reduced to the alcohol.Keywords: biorenewables; copper oxide; fatty acids; fatty alcohols; iron oxide; mesoporous silica

Palladium supported on high-surface-area ceria effectively catalyzes the hydrogenation of phenol to cyclohexanone at atmospheric pressure and room temperature. Activation of H2 at Pd sites and phenol at surface ceria sites was investigated by probing the redox properties of the catalyst and studying the mechanism of phenol adsorption. Temperature-programmed reduction and pulsed chemisorption were used to examine the effects of prereduction temperature on catalyst dispersion and reducibility. A sharp effect of prereduction temperature on catalytic activity was observed. This dependence is rationalized as a result of interactions between palladium and ceria, which under reducing conditions enhance palladium dispersion and create different types of environments around the Pd active sites and of encapsulation of the catalyst caused by support sintering at high temperatures. Temperature-programmed diffuse reflectance infrared Fourier transform spectroscopy revealed that phenol undergoes dissociative adsorption on ceria to yield cerium-bound phenoxy and water. Reduction of the chemisorbed phenoxy species decreases the number of proton-accepting sites on the surface of ceria and prevents further dissociative adsorption. Subsequent phenol binding proceeds through physisorption, which is a less active binding mode for reduction by hydrogen. High activity can be restored upon regeneration of proton acceptor sites via reoxidation/reduction of the catalyst.Keywords: dissociative adsorption; mesoporous ceria; metal−support interactions; phenol hydrogenation; redox-active support

The relative rates of the aldol reaction catalyzed by supported primary and secondary amines can be inverted by 2 orders of magnitude, depending on the use of hexane or water as a solvent. Our analyses suggest that this dramatic shift in the catalytic behavior of the supported amines does not involve differences in reaction mechanism, but is caused by activation of imine to enamine equilibria and stabilization of iminium species. The effects of solvent polarity and acidity were found to be important to the performance of the catalytic reaction. This study highlights the critical role of solvent in multicomponent heterogeneous catalytic processes.Keywords: aldol condensation; enamine catalysis; mesoporous silica nanoparticles; solid-state NMR; solvent effects

A hybrid adsorbent-catalytic nanostructured material consisting of aminopropyl groups and nickel nanoparticles immobilized in mesoporous silica nanoparticles (AP-Ni-MSN) was employed to selectively capture free fatty acids (FFAs) and convert them into saturated hydrocarbons. The working principle of these sorbent-catalytic particles was initially tested in the hydrogenation of oleic acid. Besides providing selectivity for the capture of FFAs, the adsorbent groups also affected the selectivity of the hydrogenation reaction, shifting the chemistry from hydrocracking-based (Ni) to hydrotreating-based and improving the carbon economy of the process. This approach was ultimately evaluated by the selective sequestration of FFAs from crude microalgal oil and their subsequent conversion into liquid hydrocarbons, demonstrating the suitability of this design for the refinery of renewable feedstocks.Keywords: biofuel; biorenewable feedstock; hydrotreatment; mesoporous silica nanoparticles; microalgae

We report a gold nanoparticle (AuNP)-capped mesoporous silica nanoparticle (Au-MSN) platform for intracellular codelivery of an enzyme and a substrate with retention of bioactivity. As a proof-of-concept demonstration, Au-MSNs are shown to release luciferin from the interior pores of MSN upon AuNP uncapping in response to disulfide-reducing antioxidants and codeliver bioactive luciferase from the PEGylated exterior surface of Au-MSN to Hela cells. The effectiveness of luciferase-catalyzed luciferin oxidation and luminescence emission in the presence of intracellular ATP was measured by a luminometer. Overall, the chemical tailorability of the Au-MSN platform to retain enzyme bioactivity, the ability to codeliver enzyme and substrate, and the potential for imaging tumor growth and metastasis afforded by intracellular ATP- and glutathione-dependent bioluminescence make this platform appealing for intracellular controlled catalysis and tumor imaging.

The interactions of mesoporous silica nanoparticles (MSNs) of different particle sizes and surface properties with human red blood cell (RBC) membranes were investigated by membrane filtration, flow cytometry, and various microscopic techniques. Small MCM-41-type MSNs (∼100 nm) were found to adsorb to the surface of RBCs without disturbing the membrane or morphology. In contrast, adsorption of large SBA-15-type MSNs (∼600 nm) to RBCs induced a strong local membrane deformation leading to spiculation of RBCs, internalization of the particles, and eventual hemolysis. In addition, the relationship between the degree of MSN surface functionalization and the degree of its interaction with RBC, as well as the effect of RBC−MSN interaction on cellular deformability, were investigated. The results presented here provide a better understanding of the mechanisms of RBC−MSN interaction and the hemolytic activity of MSNs and will assist in the rational design of hemocompatible MSNs for intravenous drug delivery and in vivo imaging.Keywords (): deformability; interaction; internalization; mesoporous silica nanoparticle (MSN); red blood cell (RBC) membrane; size; surface functionality

The structural properties of mesoporous silica nanoparticles are reviewed. Different strategies for the introduction of functional groups are considered. Based on the architectural features of the material, the functionalization at defined regions of the particles is described, along with the properties emerging from the corresponding site-specific modifications of their chemistry. Many applications derived from the unique architecture and chemistry of these nanostructured composite materials are shown.

•Supported iron nanoparticles catalyze the hydrodeoxygenation of fatty acids.•The catalyst favors heavily hydrodeoxygenation over decarbonylation.•The reaction proceeds through a reverse Mars–Van-Krevelen mechanism.•The degree of oxidation of Fe controls the selectivity of the reaction.•The Fe catalyst was successfully used for hydroprocessing crude microalgal oil.Iron nanoparticles supported on mesoporous silica nanoparticles (Fe-MSN) catalyze the hydrotreatment of fatty acids with high selectivity for hydrodeoxygenation over decarbonylation and hydrocracking. The catalysis is likely to involve a reverse Mars–Van Krevelen mechanism, in which the surface of iron is partially oxidized by the carboxylic groups of the substrate during the reaction. The strength of the metal–oxygen bonds that are formed affects the residence time of the reactants facilitating the successive conversion of carboxyl first into carbonyl and then into alcohol intermediates, thus dictating the selectivity of the process. The selectivity is also affected by the pretreatment of Fe-MSN, the more reduced the catalyst the higher the yield of hydrodeoxygenation product. Fe-MSN catalyzes the conversion of crude microalgal oil into diesel-range hydrocarbons.Graphical abstractDownload high-res image (95KB)Download full-size image

In this study, we demonstrate how materials science can be combined with the established methods of organic chemistry to find mechanistic bottlenecks and redesign heterogeneous catalysts for improved performance. By using solid-state NMR, infrared spectroscopy, surface and kinetic analysis, we prove the existence of a substrate inhibition in the aldol condensation catalyzed by heterogeneous amines. We show that modifying the structure of the supported amines according to the proposed mechanism dramatically enhances the activity of the heterogeneous catalyst. We also provide evidence that the reaction benefits significantly from the surface chemistry of the silica support, which plays the role of a co-catalyst, giving activities up to two orders of magnitude larger than those of homogeneous amines. This study confirms that the optimization of a heterogeneous catalyst depends as much on obtaining organic mechanistic information as it does on controlling the structure of the support.Graphical abstractAminopropyl-functionalized mesoporous silica displays a moderate catalytic activity for the aldol condensation. The reason behind this low activity is a substrate inhibition, as determined by kinetic, infrared and solid-state NMR analyses. Small widening of the pores of the support and structural modifications to the supported amine lead to dramatic improvements in catalytic activity. Cooperative interactions make this heterogeneous catalyst orders of magnitude more active than the corresponding homogeneous catalyst.Download high-res image (124KB)Download full-size imageHighlights► Aminoalkyl-silicas suffer substrate inhibition in catalysis of aldol condensation. ► An increase of only 0.8 nm in pore width improved conversion more than 20-fold. ► Poisoning by Schiff base was identified by kinetics, NMR, infrared spectroscopies. ► Replacing primary amine by secondary eliminates inhibition. ► Heterogeneous catalyst is orders of magnitude faster than homogeneous.

•Liquid flow transfer hydrogenation of phenol performed over Pd/CeO2 and Pd/Ce-Na.•Pd/Ce-Na shows 6× higher activity than Pd/CeO2.•Water-stable sodium species seemingly exist as subsurface carbonate spectators.•Na-modification increases the number of substrate adsorption and redox active sites.•High apparent activation energies reflect propanol adsorption barrier in the presence of phenol.Ceria (CeO2) and sodium-modified ceria (Ce-Na) were prepared through combustion synthesis. Palladium was deposited onto the supports (Pd/CeO2 and Pd/Ce-Na) and their activity for the aqueous-phase transfer hydrogenation of phenol using 2-propanol under liquid flow conditions was studied. Pd/Ce-Na showed a marked increase (6×) in transfer hydrogenation activity over Pd/CeO2. Material characterization indicated that water-stable sodium species were not doped into the ceria lattice, but rather existed as subsurface carbonates. Modification of ceria by sodium provided more adsorption and redox active sites (i.e. defects) for 2-propanol dehydrogenation. This effect was an intrinsic property of the Ce-Na support and independent of Pd. The redox sites active for 2-propanol dehydrogenation were thermodynamically equivalent on both supports/catalysts. At high phenol concentrations, the reaction was limited by 2-propanol adsorption. Thus, the difference in catalytic activity was attributed to the different numbers of 2-propanol adsorption and redox active sites on each catalyst.Download high-res image (103KB)Download full-size image

The structural properties of mesoporous silica nanoparticles are reviewed. Different strategies for the introduction of functional groups are considered. Based on the architectural features of the material, the functionalization at defined regions of the particles is described, along with the properties emerging from the corresponding site-specific modifications of their chemistry. Many applications derived from the unique architecture and chemistry of these nanostructured composite materials are shown.

Deposition of trimethylphosphate onto ceria followed by thermal treatment resulted in the formation of surface phosphates with retention of the ceria fluorite structure. The structural and chemical properties of the phosphate-functionalized ceria were studied using 31P solid-state NMR, XPS, zeta titration, ammonia thermal desorption, pyridine adsorption, and model reactions. The introduction of phosphates generated Brønsted acid sites and decreased the number of Lewis acid sites on the surface. The relative amount of Lewis and Brønsted acids can be controlled by the amount of trimethylphosphate used in the synthesis. Upon deposition of Pd, the multifunctional material showed enhanced activity for the hydrogenolysis of eugenol and guaiacol compared to Pd on the unmodified ceria support. This was attributed to the cooperativity between the Lewis acid sites, which activate the substrate for dearomatization, and the redox/Brønsted acid properties, which catalyze hydrogenolysis.