The huge amount of glycerol obtained during the production of biofuels has led to the search of alternatives for the use of this by-product. New applications for this polyol as a low-cost raw material need to be developed and existing ones need to be expanded. To address this problem, production of value-added molecules from crude glycerol is an effective alternative method for its disposal by incineration. Thus, the ready bioavailability, renewability and unique structure of glycerol make it a particularly attractive starting point for the production of a large number of specialty chemicals. The main purpose of this review is to focus on the catalytic reactivity of different kinds of catalysts in oxidation, dehydration, acetylation, etherification, esterification, acetalization, and ammoxidation process of glycerol conversion. Typical products are citric acid, lactic acid, 1,3-dihydroxyacetone, 1,3-propanediol, dichloro-2-propanol, acrolein, hydrogen, and ethanol. Recent studies on the catalysts, reaction conditions and possible pathways are primarily discussed.

Catalytic conversion of biodiesel derived raw glycerol to value added products

Comparative study of Ni, Co, Cu supported on γ-alumina catalysts for hydrogen production via the glycerol steam reforming reaction

Bulk nickel aluminate (NiAl2O4) was synthesised by co-precipitation at a Ni/Al mole ratio of 1:2 (stoichiometric ratio). The prepared sample was reduced at different temperatures, in the 300 to 850 °C range, and obtained assays were analysed by a wide range of analytical techniques (XFR, XRD, H2-chemisoprtion, H2-TPR, DRS UV–vis NIR, FTIR, 27Al MAS NMR, NH3-TPD, CO2-TPD, TPO) and tested for the APR of glycerol. The spinel precursor allowed the formation of small and stable Ni particles (

Nickel aluminate spinel-derived catalysts for the aqueous phase reforming of glycerol: Effect of reduction temperature

The production of lactic acid from glycerol has been receiving a lot of attention due to the efficient roles of glycerol as raw material in producing various useful chemicals. Selective oxidation and hydrothermal reactions using solid catalyst have been found as potential techniques in producing high selectivity of lactic acid. Typically, glycerol reaction mechanisms are proposed based on oxidative dehydrogenation, dehydration and benzylic acid rearrangement step in alkaline aqueous medium. Bifunctionals catalyst are useful to carry out multi-step reaction requiring different active sites in one pot reaction. One of the selective oxidation processes is using bifunctional catalyst with acidic site in combination with Al3+ or Cr3+, with Lewis acid sites and a redox centre i.e. polyoxometalates (POM) exhibited high activity (93.7%) and selectivity (90.5%) to lactic acid. Meanwhile, hydrothermal reaction by using 30%CuO/ZrO2 gave 100% glycerol conversion and 94.6% selectivity to lactic acid. Currently, the development of efficient catalysts through suitable combinations of nonprecious metals is highly proposed. This paper critically reviews the recent progress in this area of research by classifiying catalysts based on active sites and roles of catalyst characteristics. The detail discussion on the influencing parameters to enhance the selectivity of lactic acid and glycerol conversion is also provided in detail.

Production of lactic acid from glycerol via chemical conversion using solid catalyst: A review

The effects of CeO 2 -Al 2 O 3 mixed oxide preparation methods on the physical and chemical properties of CeO 2 -Al 2 O 3 , and the catalytic performance toward glycerol steam reforming (GSR) over the CeO 2 -Al 2 O 3 -supported Ni catalysts were investigated. Three CeO 2 -Al 2 O 3 supports were prepared by a single-step sol-gel (SS) of ceria and alumina precursors, followed by the impregnations of ceria precursors on both a xerogel Al 2 O 3 (IS) and a commercial Al 2 O 3 (IC). The characterization techniques used were N 2 adsorption-desorption, H 2 -chemisorption, XRD, H 2 -TPR, NH 3 -TPD, XANES, XPS and TGA. The sol-gel derived supports generate not only a well-developed mesoporous structure, but also the incorporation of the Ce species into the Al 2 O 3 structure forming CeAlO 3 perovskite. This formation suppresses the interaction between Ni and Al 2 O 3 , thereby increasing the number of active and Bronsted acid sites to improve the bifunctional metal-acid properties of Ni/CeO 2 -Al 2 O 3 in the hydrogenolysis and dehydrogenation-dehydration of condensable intermediates that produce more H 2 . The formation of CeAlO 3 is remarkably promoted by the single-step sol-gel preparation method, and the catalyst supported on the SS-derived oxide exhibits excellent activity and strong resistances to coke formation, phase transformation, and nickel sintering.

Remarkable activity and stability of Ni catalyst supported on CeO2-Al2O3 via CeAlO3 perovskite towards glycerol steam reforming for hydrogen production

The conversion of glycerol in gas phase and atmospheric pressure has been investigated over 10 wt.% Ni/γ-Al2O3 catalyst. The catalysts were prepared with nickel nitrate and pre-treated with hydrogen in the range of 623–1073 K. The resultant catalysts were characterized by N2-physisoption, H2-chemisorption, X-ray diffraction (XRD), TGA-MS, TEM, RAMAN, NH3-TPD, XPS, TPO-MS and XANES. The stability and the catalytic behavior of the catalysts were affected by the reduction pre-treatment. Glycerol reaction pathways were proposed based on dehydration, dehydrogenation and hydrogenolysis steps. The main products identified were: hydroxyacetone, pyruvaldehyde, pyruvic acid, lactic acid, lactide, acetaldehyde and methane. The number of exposed Ni atoms and the degree of reduction of the NiO species affected the hydrogenolysis reaction of glycerol to CH4 affecting the catalytic stability. The catalyst was deactivated by coke formation, by transformation of Ni phase to nickel carbide (Ni3C), as well as by oxidation of the Ni phase during the reaction. In addition, Raman analysis revealed two types of carbonaceous deposits over the used samples: on the Ni species and on the support. The regeneration treatment by oxidation–reduction reactivated the catalyst successfully.

F. López Bonillo

Papers

Conversion of glycerol over 10%Ni/γ-Al2O3 catalyst