Single-atom metal-nitrogen-carbon (M-N-C) catalysts have sparked intensive interests, however, the development of an atomically dispersed metal-phosphorus-carbon (M-P-C) catalyst has not been achieved, although molecular metal-phosphine complexes have found tremendous applications in homogeneous catalysis. Herein, we successfully construct graphitic phosphorus species coordinated single-atom Fe on P-doped carbon, which display outstanding catalytic performance and reaction generality in the heterogeneous hydrogenation of N-heterocycles, functionalized nitroarenes, and reductive amination reactions, while the corresponding atomically dispersed Fe atoms embedded on N-doped carbon are almost inactive under the same reaction conditions. Furthermore, we find that the catalytic activity of graphitic phosphorus coordinated single-atom Fe sharply decreased when Fe atoms were transformed to Fe clusters/nanoparticles by post-impregnation Fe species. This work can be of fundamental interest for the design of single-atom catalysts by utilizing P atoms as coordination sites as well as of practical use for the application of M-P-C catalysts in heterogeneous catalysis.
Bimetallic
catalysts based on nonprecious transition metals have
attracted increasing attention because of their unique synergistic
effects in catalytic reactions, but the understanding of the nature
of synergistic effects and their roles in a specific hydrogenation
reaction remains lacking. Herein, a series of bimetallic Cu
x
Co
y
/Al2O3 (x/y = 5:1, 2:1, 1:1, 1:2,
1:5) nanocomposite catalysts were fabricated via the successive calcination
and reductive activation process of layered double hydroxide precursors.
Their catalytic performance in the selective hydrogenation of bioderived
ethyl levulinate to 1,4-pentanediol (1,4-PeD) depended sensitively
on the chemical composition of bimetallic CuCo catalysts. The optimal
bimetallic Cu2Co1/Al2O3 catalyst exhibited markedly improved catalytic activity and selectivity
compared to monometallic Cu/Al2O3, as confirmed
by its lower apparent activation energy barrier of 65.1 kJ mol–1 of the rate-determining step and its high selectivity
of 93% to 1,4-PeD. Detailed characterization analyses and intrinsic
catalytic studies revealed that the presence of CoO
x
species in the bimetallic Cu
x
Co
y
/Al2O3 catalysts enhanced
the metallic Cu dispersion and H2 activation ability. More
importantly, the strong electronic interaction at the interface of
Cu and adjacent CoO
x
species modified
the chemical states of Cu species to create proper surface Cu0/Cu+ distributions and, particularly, provided
synergic catalysis sites of Cu and electron-deficient CoO
x
species, which was primarily responsible for the
excellent catalytic performance of bimetallic CuCo catalysts. The
bimetallic CuCo catalysts exhibited good stability in both batch and
fixed-bed continuous flow reactions. Furthermore, present CuCo nanocomposite
catalyst could be applied to the highly selective hydrogenation of
other carboxylic esters and lactones to synthesize valuable C4, C5,
and C6 diols.
Considerable effort has been applied to the development of new processes and catalysts for cellulose conversion to valuable platform chemicals. Isosorbide is among the most interesting products as it can be applied as a monomer and building block for the future replacement of fossil resource-based products. A sustainable method of isosorbide production from cellulose is presented in this work. The strategy relies on a bifunctional Ru catalyst supported on mesoporous niobium phosphate in a H2 atmosphere under pressure without further addition of any soluble acid. Over 50 % yield of isosorbide with almost 100 % cellulose conversion can be obtained in 1 h. The large surface area, pore size, and strong acidity of mesoporous niobium phosphate promote the hydrolysis of cellulose and dehydration of sorbitol; additionally, the appropriate size of the supported Ru nanoparticles avoids unnecessary hydrogenolysis of sorbitol. Under a cellulose/catalyst mass ratio of 43.3, the present bifunctional catalyst could be stably used up to six times, with its mesoporous structure well preserved and without detectable Ru leaching into the reaction solution.
Direct oxidative amination of the sp 3 C−H bond is an attractive synthesis route to obtain amides. Conventional catalytic systems for this transformation are based on transition metals and complicated synthesis processes. Herein, direct and efficient oxidative amination of the methyl C−H bond in a wide range of N-heterocycles to access the corresponding amides over metal-free porous carbon is successfully developed. To understand the fundamental structure−activity relationships of carbon catalysts, the surface functional groups and the graphitization degree of porous carbon have been purposefully tailored through doping with nitrogen or phosphorus. The results of characterization, kinetic studies, liquid-phase adsorption experiments, and theoretical calculations indicate that the high activity of the carbon catalyst is attributed to the synergistic effect of surface acidic functional groups (hydroxyl/carboxylic acid/phosphate) and more graphene edge structures exposed on the surface of carbon materials with a high graphitization degree, in which the role of acidic functional groups is to adsorb the substrate molecule and the role of the graphene edge structure is to activate O 2 .
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