There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The presence of an excessive concentration of CO2 in the atmosphere needs to be curbed with suitable measures including the reduction of CO2 emissions at stationary point sources such as power plants through carbon capture technologies and subsequent conversion of the captured CO2 into non-polluting clean fuels/chemicals using photo and/or electrocatalytic pathways. Porous materials have attracted much attention for carbon capture and in the recent past; they have witnessed significant advancements in their design and implementation for CO2 capture and conversion. In this context, the emerging trends in major porous adsorbents such as MOFs, zeolites, POPs, porous carbons, and mesoporous materials for CO2 capture and conversion are discussed. Their surface texture and chemistry, and the influence of various other features on their efficiency, selectivity, and recyclability for CO2 capture and conversion are explained and compared thoroughly. The scientific and technical advances on the material structure versus CO2 capture and conversion provide deep insights into designing effective porous materials. The review concludes with a summary, which compiles the key challenges in the field, current trends and critical challenges in the development of porous materials, and future research directions combined with possible solutions for realising the deployment of porous materials in CO2 capture and conversion.

Emerging trends in porous materials for CO2 capture and conversion

Schiff base-derived homogeneous and heterogeneous palladium catalysts for the Suzuki–Miyaura reaction

Recent advances in the Suzuki–Miyaura cross-coupling reaction using efficient catalysts in eco-friendly media

Understanding active species in catalytic transformations: From molecular catalysis to nanoparticles, leaching, “Cocktails” of catalysts and dynamic systems

Several chitosan and 6-deoxy-6-amino chitosan-Schiff base ligands ( 1 – 4 ) were prepared by condensation of either 2-pyridinecarboxaldehyde or 2-(diphenylphosphino)benzaldehyde with the amino group(s) on chitosan and its derivative (6-deoxy-6-amino chitosan). The supported ligands were reacted with [PdCl 2 (COD)] to form chitosan-supported Pd II catalysts ( 5 – 8 ). All the supported catalysts were air- and moisture-stable and have been characterized using elemental analysis, ICP-MS, UV–vis, FT-IR, PXRD, TGA, 31 P solid state NMR and TEM. As models for the heterogenized catalysts ( 5 and 6 ), mononuclear Pd II complexes ( 9 and 10 ) were also prepared via the Schiff-base condensation reaction of 1,3,4,6-tetra- O -acetyl-β- d -glucosamine hydrochloride to form 1,3,4,6-tetra- O -acetyl-β- d -glucos-2-pyridylimine and 1,3,4,6-tetra- O -acetyl-β- d -glucos-2-(diphenylphosphino)imine which were subsequently reacted with [PdCl 2 (COD)]. Complexes ( 9 and 10 ) and their precursors were characterized by 1 H and 31 P NMR, UV–vis, FT-IR spectroscopy and elemental analysis. Catalytic Suzuki–Miyaura and Heck carbon–carbon cross-coupling reactions were carried out using the supported Pd catalysts and their mononuclear analogues. The immobilized and homogeneous catalysts showed high activity for both the Suzuki–Miyaura and Heck cross-coupling reactions in organic and aqueous media. Homogeneous catalysts ( 9 and 10 ) decomposed during the first run, while the supported catalysts could be recycled and reused up to five times.

Pd nanosized particles supported on chitosan and 6-deoxy-6-amino chitosan as recyclable catalysts for Suzuki-Miyaura and Heck cross-coupling reactions

Rh(I) complexes supported on a biopolymer as recyclable and selective hydroformylation catalysts

Solvent-free conversion of bioderived levulinic acid (LA) to γ-valerolactone (GVL) has been achieved by new pyrazolylphosphite and pyrazolylphosphinite ruthenium(II) complexes as catalyst precursors, using both formic acid and molecular hydrogen as hydrogen sources. The reactions were very efficient at moderate temperatures of 100–120 °C. With a catalyst loading of 0.1%, 100% LA conversion (with hydrogen gas) was achieved with 100% GVL selectivity at 110 °C and 15 bar. The catalyst was recyclable up to three times without significant loss of activity and selectivity. The catalyst precursors are found to be more efficient when the hydrogen source was molecular hydrogen as compared to formic acid. NMR studies of reactions involving formic acid as a hydrogen source indicate that the initial step in the reaction involves the decomposition of formic acid to CO2 and H2.

Efficient Solvent-Free Hydrogenation of Levulinic Acid to γ-Valerolactone by Pyrazolylphosphite and Pyrazolylphosphinite Ruthenium(II) Complexes

Water-soluble dendritic ligands based on tris-2-(5-sulfonato salicylaldimine ethyl)amine (5) and DAB-(5-sulfonato salicylaldimine) (6) (DAB = diaminobutane) were synthesized by means of Schiff base condensation and sulfonation reactions. These dendritic ligands were fully characterized by 1H NMR, 13C NMR and FT-IR spectroscopy, elemental analysis and mass spectrometry. Dendritic ligands (5 and 6) in combination with [RhCl(COD)]2 (COD = 1,5-cyclooctadiene) were evaluated in aqueous biphasic hydroformylation of 1-octene. New water-soluble mononuclear 5-sulfonato propylsalicylaldimine Rh(I) complexes (7 and 8) were synthesized and characterized using 1H NMR, 13C NMR and FT-IR spectroscopy, elemental analysis as well as mass spectrometry. These complexes were applied as catalyst precursors in aqueous biphasic hydroformylation reactions. All the catalyst precursors were active in the hydroformylation of 1-octene under the investigated conditions. Optimal conditions were realized at 75 °C (40 bars), where the best selectivity for aldehydes was noticed. Catalyst recycling was achieved up to 5 times with minimal loss in conversion and consistent chemoselectivities and regioselectivities. Less Rh leaching was observed in the dendritic systems (5 and 6)/[RhCl(COD)]2 as compared to mononuclear catalyst precursors (7 and 8) as determined by inductively coupled plasma-mass spectrometry (ICP-MS).

Banothile C. E. Makhubela

Papers

Pd nanosized particles supported on chitosan and 6-deoxy-6-amino chitosan as recyclable catalysts for Suzuki-Miyaura and Heck cross-coupling reactions

Rh(I) complexes supported on a biopolymer as recyclable and selective hydroformylation catalysts

Efficient Solvent-Free Hydrogenation of Levulinic Acid to γ-Valerolactone by Pyrazolylphosphite and Pyrazolylphosphinite Ruthenium(II) Complexes

Aqueous-phase hydroformylation of 1-octene using hydrophilic sulfonate salicylaldimine dendrimers.

Synthesis, characterisation and reactivity of water-soluble ferrocenylimine-Rh(I) complexes as aqueous-biphasic hydroformylation catalyst precursors