Applications of renewable biomass provide facile routes to alleviate the shortage of fossil fuels as well as to reduce the emission of CO2. Glycerol, which is currently produced as a waste in the biodiesel production, is one of the most attractive biomass resources. In the past decade, the conversion of glycerol into useful chemicals has attracted much attention, and glycerol is mainly converted by steam reforming, hydrogenolysis, oxidation, dehydration, esterification, carboxylation, acetalization, and chlorination. In this review, we focused on the catalytic hydrogenolysis of glycerol into C3 chemicals, which contain many industrially important products such as 1,2-propanediol, 1,3-propanediol, allyl alcohol, 1-propanol and propylene. In the hydrogenolysis of glycerol into propanediols, advantages and disadvantages of liquid- and vapor-phase reactions are compared. In addition, recent studies on catalysts, reaction conditions, and proposed pathways are primarily summarized and discussed. Furthermore, new research trends are introduced in connection with the hydrogenolysis of glycerol into allyl alcohol, propanols and propylene.

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Glycerol hydrogenolysis into useful C3 chemicals

Heterogeneous single-atom catalyst (SAC) opens a unique entry to establishing structure-performance relationship at the molecular level similar to that in homogeneous catalysis. The challenge lies in manipulating the coordination chemistry of single atoms without changing single-atom dispersion. Here, we develop an efficient synthetic method for SACs by using ethanediamine to chelate Pt cations and then removing the ethanediamine by a rapid thermal treatment (RTT) in inert atmosphere. The coordination chemistry of Pt single atoms on a Fe2O3 support is finely tuned by merely adjusting the RTT temperature. With the decrease in Pt-O coordination number, the oxidation state of Pt decreases, and consequently the hydrogenation activity increases to a record level without loss of chemoselectivity. The tunability of the local coordination chemistry, oxidation states of the metal, and the catalytic performance of single atoms reveals the unique role of SACs as a bridge between heterogeneous and homogeneous catalysis.

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Unraveling the coordination structure-performance relationship in Pt 1 /Fe 2 O 3 single-atom catalyst.

Pd–Ag alloy catalysts with very dilute amounts of Pd were synthesized. EXAFS results demonstrated that when the concentration of Pd was as low as 0.01 wt %, Pd was completely dispersed as isolated single atoms in Ag nanoparticles. The activity for the hydrogenation of acrolein was improved by the presence of these isolated Pd atoms due to the creation of sites with lower activation energy for H2 dissociation. In addition, for the same particle size, the 0.01% Pd/8% Ag alloy nanoparticles exhibited higher selectivity than their monometallic counterparts, suggesting that the Pd atom may act as a site for the favorable bonding of the acrolein molecule for facile hydrogenation of the aldehyde functionality.

Single-Atom Alloy Pd–Ag Catalyst for Selective Hydrogenation of Acrolein

The metal-catalyzed selective hydrogenation of biomass-derived molecules is in great demand but is challenging due to the complex reaction pathways. Herein, we report a persuasive example for achieving selective hydrogenation of furfural over Pd catalysts by controllable sorption of molecules in zeolite micropores. The key to this success is fixation of Pd nanoparticles inside of silicalite-1 zeolite with controllable wettability (Pd@S-1-OH) by functionalizing silanol groups into the zeolite framework. In the hydrogenation of furfural as a model reaction, the Pd@S-1-OH catalyst with appropriate hydrophilicity exhibits extraordinary selectivity for the formation of furan, giving furan selectivity as high as >99.9% with a complete conversion of furfural, outperforming the conventional Pd nanoparticles supported on zeolite crystals (Pd/S-1) and S-1 zeolite fixed Pd catalysts without an artificially functionalized silanol group (Pd@S-1). The extraordinary performance of Pd@S-1-OH is reasonably attributed to t...

Importance of Zeolite Wettability for Selective Hydrogenation of Furfural over Pd@Zeolite Catalysts

Well-dispersed bimetallic nanoparticles confined in mesoporous metal oxides and their optimized catalytic activity for nitrobenzene hydrogenation

Selective hydrogenation of acrolein on supported silver catalysts: A kinetics study of particle size effects

Perturbation of Reactivity with Geometry: How Far Can We Go?

Bimetallic PtPd on silica nanoparticle catalysts have been synthesized, and their average structure has been determined by Pt L3 and Pd K edge extended X-ray absorption fine-structure spectroscopy. The bimetallic structure is confirmed from elemental line scans by scanning transmission electron microscopy of the individual 2-nm-sized particles. A general method is described to determine the surface composition of bimetallic nanoparticles even when both metals adsorb; for example, CO, by combining the quantitative characterization by X-ray absorption near-edge structure spectra at L edges with CO adsorption with the adsorption stoichiometry determined by Fourier transform infrared spectroscopy. Determination of the surface composition leads to a better understanding of the changes in catalytic chemistry that accompany alloy formation. Although monometallic Pt and Pd have similar turnover rates for neopentane hydrogenolysis and isomerization, on the basis of the surface composition, it appears that in the b...

General method for determination of the surface composition in bimetallic nanoparticle catalysts from the L edge X-ray absorption near-edge spectra

PdZn catalysts have been proposed as an alternative to Cu low temperature water gas shift (WGS) catalysts due to their similar reactivity but higher thermal stability. Unfortunately, Pd based alloys are likely to be considerably more expensive than Cu catalysts. Therefore, we explore NiZn as a potentially cheaper alternative to PdZn. Both PdZn(111) and NiZn(111) have similar potential energy surfaces for WGS as previous work on Cu(111) suggesting that they may be effective WGS catalysts. However, unlike PdZn (and Cu), the primary mechanism for WGS shifts from the carboxyl mechanism to a redox mechanism over NiZn(111) (although they are similar in magnitude).

Carolina Gomez

Papers

Selective hydrogenation of acrolein on supported silver catalysts: A kinetics study of particle size effects

Perturbation of Reactivity with Geometry: How Far Can We Go?

General method for determination of the surface composition in bimetallic nanoparticle catalysts from the L edge X-ray absorption near-edge spectra

A Comparative Density Functional Theory Study of Water Gas Shift Over PdZn(111) and NiZn(111)