Hybrid Sulfonic Acid Catalysts Based on Silica-Supported Poly(Styrene Sulfonic Acid) Brush Materials and Their Application in Ester Hydrolysis

Catalytic conversions involving water as a reactant, product, or solvent are of high importance in biomass conversion into fuels and chemicals. In this context, water-tolerant solid acids are highly valued. Polymer-oxide hybrid materials based on nonporous silica-supported sulfonic acid-containing polymer brush materials are proposed here as a new class of potentially water-tolerant solid acid catalyst. Atom transfer radical polymerization (ATRP), using both (i) an established and (ii) a new ATRP initiator that is designed to improve the hydrolytic stability of the catalyst, leads to creation of poly(styrene) brushes on the surface of fumed silica. These brushes are sulfonated to produce an acid catalyst akin to an acidic Merrifield resin, but with enhanced accessibility of the active sites. The catalysts are evaluated in the hydrolysis of ethyl lactate, with the polymer brush materials having the same activity as a homogeneous catalyst, p-toluenesulfonic acid, and being substantially more active than an acidic polymer resin (Amberlyst 15). The heterogeneous nature of the catalyst allows for straightforward catalyst recovery and recycle. The stability of the polymer brush catalysts depends on the nature of the initiator used, with the new alkyl-based initiator, introduced here, giving enhanced stability relative to the standard, ester-containing initiator that is most commonly used in surface-initiated ATRP. The activity of the recycled polymer brush catalysts decreased slightly in each cycle because of both desulfonation and the gradual detachment of the polymer chains from the oxide support. Oxide-supported polymer brush materials are suggested to be a promising new architecture for hybrid catalyst materials

Modulating the Reactivity of an Organometallic Catalyst via Immobilization on a Spatially Patterned Silica Surface

Modulating the Reactivity of an Organometallic Catalyst via Immobilization on a Spatially Patterned Silica Surfac

Toward Single-Site, Immobilized Molecular Catalysts: Site-Isolated Ti Ethylene Polymerization Catalysts Supported on Porous Silica

A new, general patterning methodology that may allow for the preparation of site-isolated organometallic catalysts on a silica surface is reported. The technique is demonstrated with Group 4 polymerization catalysts. The catalysts synthesized via the patterning method have up to a 10-fold increase in activity as compared to materials prepared by traditional techniques. In addition to supporting Group 4 polymerization catalysts, the patterned aminosilica is a possible support for other metal complexes, allowing for the synthesis of a wide array of immobilized single-site organometallic catalysts

Airborne Aldehyde Abatement by Latex Coatings Containing Amine-Functionalized Porous Silicas

Amine-functionalized porous silicas (aminosilicas) are incorporated into latex coatings, and the airborne aldehyde abatement abilities of the dried applied films are examined. The aminosilicas in the resulting dried films are uniformly dispersed inside the latex component, and they are demonstrated to be effective adsorbents for airborne aldehydes. The latex component does not hinder the adsorption capacities of the aminosilicas, with the adsorbed amounts being similar to those of the original aminosilica powders before incorporation into the latex. However, the adsorption rates are slowed after incorporation of the aminosilicas into the films, relative to that of the powder samples. Overall, the aminosilica-incorporated latex films are demonstrated to be effective aldehyde-abating materials

Stability of Supported Amine Adsorbents to SO₂ and NO_<i>x</i> in Postcombustion CO₂ Capture. 2. Multicomponent Adsorption

Packed bed CO₂ adsorption breakthrough experiments using both amine-impregnated and amine-grafted silica adsorbent materials in the presence of SO₂, NO and NO₂ impurities are reported. The effects of temperature, feed concentration and adsorbent amine loading on the dynamic adsorption capacity of the adsorbents are evaluated by performing dual component SO₂/CO₂, NO/CO₂ and NO₂/CO₂ coadsorption experiments as well as three component SO₂/NO/CO₂ adsorption experiments. Although SO₂ is found to significantly influence the dynamic CO₂ capacity of aminosilica adsorbents, the obtained results confirm the long-term stability of the adsorbents during SO₂/CO₂ coadsorption runs when the bed is not allowed to fully saturate with SO₂. On the other hand, little competitive effect of NO on CO₂ adsorption is observed in any case. This is due to the decreased affinity of amine-based adsorbents toward NO as opposed to SO₂. The more reactive nitrogen oxide, NO₂, is shown to have a minimal impact on CO₂ adsorption when it is present at low levels in the simulated flue gas. Among the adsorbents investigated, the results demonstrate that secondary amine containing adsorbents are more stable to SO_<i>x</i> and NO_<i>x</i> impurities in CO₂ capture processes than those that contain primary amine groups

Amine-Functionalized Porous Silicas as Adsorbents for Aldehyde Abatement

A series of aminopropyl-functionalized silicas containing of primary, secondary, or tertiary amines is fabricated via silane-grafting on mesoporous SBA-15 silica and the utility of each material in the adsorption of volatile aldehydes from air is systematically assessed. A particular emphasis is placed on low-molecular-weight aldehydes such as formaldehyde and acetaldehyde, which are highly problematic volatile organic compound (VOC) pollutants. The adsorption tests demonstrate that the aminosilica materials with primary amines most effectively adsorbed formaldehyde with an adsorption capacity of 1.4 mmol_HCHO g^–1, whereas the aminosilica containing secondary amines showed lower adsorption capacity (0.80 mmol_HCHO g^–1) and the aminosilica containing tertiary amines adsorbed a negligible amount of formaldehyde. The primary amine containing silica also successfully abated higher aldehyde VOC pollutants, including acetaldehyde, hexanal, and benzaldehyde, by effectively adsorbing them. The adsorption mechanism is investigated by ¹³C CP MAS solid-state NMR and FT-Raman spectroscopy, and it is demonstrated that the aldehydes are chemically attached to the surface of aminosilica in the form of imines and hemiaminals. The high aldehyde adsorption capacities of the primary aminosilicas in this study demonstrate the utility of amine-functionalized silica materials for reduction of gaseous aldehydes

Optimized Cellulose Nanocrystal Organocatalysts Outperform Silica-Supported Analogues: Cooperativity, Selectivity, and Bifunctionality in Acid–Base Aldol Condensation Reactions

Cellulose nanocrystals (CNCs) are demonstrated as effective, ordered supports for cooperative acid–base heterogeneous organocatalysis, offering an alternative to typical silica supports. CNC catalyst surface chemistry is optimized through quantitative control of the loadings of carboxylic acids, primary amines, and sulfate half-esters, as characterized by elemental analysis, conductometric titration, and FT–IR spectroscopy. Catalysts are evaluated in the liquid phase aldol condensation of 4-nitrobenzaldehyde or furfural with acetone. Carboxylic acids are effective cooperative acid partners in CNC organocatalysts, and site-specific activity is strongly correlated with the COOH:NH2 ratio. Partial sulfate half-ester removal, high acid/base ratios, and use of unprotected diamines in the catalyst synthesis lead to optimized CNC catalyst function (site-time yield = 1.0 × 10–4 s–1). High selectivities to dehydrated aldol products (>80%) are achieved due to the acid content of the CNC catalysts. CNC catalysts outperform analogous SBA-15-supported aminosilica catalysts in regard to both activity and selectivity. Crystalline surface structures and ordered chemical functionalization in CNCs appear advantageous for precise design and control of bifunctional acid–base cooperative catalysts

Ring-Expanding Olefin Metathesis: A Route to Highly Active Unsymmetrical Macrocyclic Oligomeric Co-Salen Catalysts for the Hydrolytic Kinetic Resolution of Epoxides

In the presence of the third generation Grubbs catalyst, the ring-expanding olefin metathesis of a monocyclooct-4-en-1-yl functionalized salen ligand and the corresponding Co(II)(salen) complex at low monomer concentrations results in the exclusive formation of macrocyclic oligomeric structures with the salen moieties being attached in an unsymmetrical, flexible, pendent manner. The TOF-MALDI mass spectrometry reveals that the resulting macrocyclic oligomers consist predominantly of dimeric to tetrameric species, with detectable traces of higher homologues up to a decamer. Upon activation under aerobic and acidic conditions, these Co(salen) macrocycles exhibit extremely high reactivities and selectivities in the hydrolytic kinetic resolution (HKR) of a variety of racemic terminal epoxides under neat conditions with very low catalyst loadings. The excellent catalytic properties can be explained in terms of the new catalyst's appealing structural features, namely, the flexible oligomer backbone, the unsymmetrical pendent immobilization motif of the catalytic sites, and the high local concentration of Co(salen) species resulting from the macrocyclic framework. This ring-expanding olefin metathesis is suggested to be a simple way to prepare tethered metal complexes that are endowed with key features(i) a high local concentration of metal complexes and (ii) a flexible, single point of attachment to the supportthat facilitate rapid and efficient catalysis when a bimetallic transition state is required

Steam Induced Structural Changes of a Poly(ethylenimine) Impregnated γ‑Alumina Sorbent for CO₂ Extraction from Ambient Air

Poly­(ethylenimine) (PEI) impregnated mesoporous γ-alumina sorbents are utilized for CO₂ adsorption from dry and humid simulated ambient air, and the sorbents are regenerated under an environment of flowing steam for times ranging from 5 min to 24 h of continuous exposure. The sorbents are compared on the basis of equilibrium CO₂ capacities from simulated air at 400 ppm of CO₂, 50% relative humidity, and 30 °C as well as their physiochemical characterization by means of X-ray diffraction (XRD), ²⁷Al NMR spectroscopy, IR spectroscopy, Raman spectroscopy, N₂ physisorption, and elemental analysis. The sorbents retain better than 90% of the initial equilibrium capacity of ∼1.7 mmol/g at steam exposure times up to 12 h; however, PEI leaching reduced the capacity of the sorbent to 0.66 mmol/g after 24 h of continuous treatment. It is demonstrated that the γ-alumina support partially hydrates to form a boehmite crystal phase at steam times of 90 min and longer but that this phase transition occurs predominately between 90 min and 12 h of steam treatment, slowing at longer times of 12 and 24 h of treatment. Evidence is presented to suggest that the presence of boehmite on the sorbent surface does not significantly alter the amine efficiency of impregnated PEI. The collected results suggest that γ-alumina/PEI composite materials are promising sorbents for CO₂ capture from ambient air with regeneration in flowing steam