Catalytic phosphorus(V)-mediated chlorination and bromination reactions of alcohols have been developed. The new reactions constitute a catalytic version of the classical Appel halogenation reaction. In these new reactions oxalyl chloride is used as a consumable stoichiometric reagent to generate the halophosphonium salts responsible for halogenation from catalytic phosphine oxides. Thus, phosphine oxides have been transformed from stoichiometric waste products into catalysts and a new concept for catalytic phosphorus-based activation and nucleophilic substitution of alcohols has been validated. The present study has focused on a full exploration of the scope and limitations of phosphine oxide catalyzed chlorination reactions as well as the development of the analogous bromination reactions. Further mechanistic studies, including density functional theory calculations on proposed intermediates of the catalytic cycle, are consistent with a catalytic cycle involving halo- and alkoxyphosphonium salts as intermediates.

We describe a compactivation approach, which incorporates a mechanical compression step before thermochemical activation, to carbons that possess higher porosity than analogous conventionally activated carbons but without any significant changes in pore size. The method works for both highly activated and lowly activated carbons. For highly compactivated carbons (thermal treatment at 800 o C), enhanced porosity (surface area and pore volume up to 4000 m 2 g -1 and 3.0 cm 3 g -1 ) is achieved along with superior hydrogen uptake of 7.3 wt% (at -196ºC and 20 bar), rising to 9.6 wt% at 40 bar and 14.2 wt% at 150 bar, which corresponds to volumetric uptake of 38 g l -1 at 40 bar and 56 g l -1 at 150 bar, while at room temperature uptake reaches 3.6 wt% (14 g l -1 ). On densification, the highly compactivated carbons can retain a much greater proportion of their porosity (3200 -3500 m 2 g -1 and 2.0 -2.7 cm 3 g -1 ) whilst attaining high packing density, which translates to exceptional volumetric hydrogen storage; 49 g l -1 at 40 bar, 60 g l -1 at 80 bar and 72 g l -1 at 150 bar and -196 o C, while at room temperature and 150 bar the densified carbons can store 3.4 wt% (18 g l -1 ). For lowly activated carbons (thermal treatment at 600 o C), compactivation yields carbons with 35% higher surface area and pore volume but with no pore size expansion. The increase in surface area arising from small (5.9 Å) micropores results in a dramatic increase in CO2 storage capacity; at 25 o C the CO2 uptake rises from 1.3 to 2.1 mmol g -1 at 0.15 bar, and from 3.4 to 5.5 mmol g -1 at 1 bar. Due to their lowly activated nature, the highly microporous compactivated carbons have high packing density and thus exhibit very high volumetric CO2 uptake of 79 g l -1 and 206 g l -1 at 0.15 and 1 bar, respectively (cf to 52 g l -1 and 136 g l -1 for conventionally activated analogue).

The relative influence of nitrogen doping and pore size of highly microporous carbon materials, with virtually identical porosity, on CO2 uptake capacity at low pressure (≤1 bar) is presented in this article. The carbon materials are prepared via a range of synthesis methods, including activation of a variety of carbon precursors (biomass, polypyrrole, or carbon nanotube superstructures) and carbonization of an organic salt (potassium hydrogen phthalate), which generated a series of carbons with closely matched porosity but which are either N-free or N-doped. The carbons have a total surface area of 920 ± 60 m2/g and micropore surface area of 860 ± 40 m2/g, values that are within ±5% of each other and within the repeatability range (or experimental error) of the porosity measurements. The carbons have identical micropore volume of 0.39–0.40 cm3/g, and similar overall pore size and apparent pore size distribution. The similar porosity values allowed a simple and straightforward analysis of the influence of N-doping on CO2 uptake without any ambiguities associated with changes in surface area and pore volume. Contrary to many previous reports wherein both N-doping and porosity varied, we show that the presence of N has no beneficial effect on the adsorption of CO2. Rather, we show that the low-pressure adsorption of CO2 on carbons is critically sensitive to the pore size, and in particular to minute changes in micropore size distribution within the pore size range 5–10 Å. The pore size also exerts greater influence on both the isosteric heat of CO2 adsorption and the selectivity for CO2 over N2.

Carbon nanotube (CNT) superstructures prepared at 180 °C are activated to highly porous (1479–3802 m2g−1; 0.83–2.98 cm3g−1) carbons with excellent CO2uptake; up to 4.8 and 8.4 mmol g−1at 1 bar and 25 or 0 °C, respectively, and exceptional hydrogen storage; up to 7.5 and 14.9 wt% at −196 °C and 20 or 150 bar, respectively, and 4.4 wt% at 25 °C and 150 bar.