Aqueous Phase Reforming Of Glycerol Research Articles

Hydrogenolysis of glycerol over supported bimetallic Ni/Cu catalysts with and without external hydrogen addition in a fixed-bed flow reactor

The role of high hydrogen pressure in the hydrogenolysis of glycerol to 1,2-propanediol has been studied extensively. Given the peculiar properties of hydrogen such as its inflammability and explosibility, the hydrogenolysis of glycerol without external hydrogen addition seems a more advantageous option. This study focuses on the conversion of glycerol to 1,2-propanediol over different supported bimetallic Ni/Cu catalysts in a fixed-bed flow reactor, using in situ hydrogen production and external hydrogen. Among the catalysts prepared, Ni/Cu/TiO2 catalyst was observed to efficiently catalyze the hydrogenolysis of glycerol to 1,2-propanediol under N2 pressure using 2-propanol as hydrogen source. This was due to the high Cu dispersion and Ni/Cu atomic ratio on the catalyst surface. However, the experimental results indicated that the effect of catalyst acid sites on glycerol hydrogenolysis was more noticeable when the reaction was performed under H2 pressure. The metal active sites of the catalyst played a significant role in the hydrogen production and also affected the glycerol hydrogenolysis with hydrogen produced from 2-propanol catalytic transfer hydrogenation (CTH) and glycerol aqueous phase reforming (APR). The stability study revealed that the Ni/Cu/TiO2 catalyst underwent serious deactivation during the hydrogenolysis of glycerol. The characterization results showed that the metal leaching and metal particles sintering were responsible for the catalyst deactivation when the glycerol hydrogenolysis was conducted using water as a solvent. However, the activity loss for reactions performed using 2-propanol as a solvent was mainly related to the metal particles sintering and the presence of adsorbed species on the catalyst surface.

In-situ glycerol aqueous phase reforming and phenol hydrogenation over Raney Ni®

In-situ glycerol aqueous phase reforming and phenol hydrogenation (IGAPH) was conducted with Raney Ni® at 180–240 °C for phenol to glycerol ratios from 0 to 4.88. Thermodynamic analysis of the complex IGAPH reaction system revealed the need to balance endothermic glycerol aqueous phase reforming (APR) and exothermic phenol hydrogenation reactions. It was found that maximum glycerol carbon selectivity for APR and maximum hydrogen selectivity for phenol hydrogenation occurred at 220 °C. Addition of phenol to glycerol APR increased glycerol conversion and glycerol carbon selectivity for APR. These observations can be attributed to an equilibrium shift to the forward APR reaction due to hydrogen consumption and suppression of competing parallel reactions by phenol hydrogenation. An initial rate model of the system suggests that IGAPH proceeds via the Langmuir-Hinshelwood mechanism and is rate-limited by phenol hydrogenation. Perspectives for future process development in terms of reaction heat and catalyst stability are provided.

K-Promoted Pt-Hydrotalcite Catalyst for Production of H2 by Aqueous Phase Reforming of Glycerol

The effect of potassium on the Pt supported hydrotalcite catalyst (Pt-KHT) was investigated in the aqueous phase reforming (APR) of glycerol for the efficient production of H2. Pt-KHT was prepared by the sequential incipient wetness impregnation method where impregnation of K was carried out first followed by incorporation of Pt. The catalyst was characterized by XRD, SEM, HRTEM, XPS, FTIR, TPR, and TPD. The TEM images of the catalyst showed highly dispersed Pt-species supported on hydrotalcite with needle-like structure. The addition of potassium (K+) increases the basicity of the Pt-KHT catalyst and enhances the production of hydrogen through APR of glycerol. The gaseous product formed over Pt-KHT at 250 °C was 99.4% which is higher than that obtained of Pt-HT catalyst, and an H2 selectivity of 67.4% was achieved over Pt-KHT after 3 h of reaction.

Production of renewable hydrogen through aqueous-phase reforming of glycerol over Ni/Al2O3[sbnd]MgO nano-catalyst

In this study, a series of Ni nano-catalysts supported on Al2O3 and MgO were prepared through the co-precipitation technique. Effects of the Al/Mg ratio on physicochemical characteristics of Ni/Al2O3MgO catalysts were examined. Moreover, catalytic performance was investigated in order to determine the optimum catalyst for H2 production in aqueous phase reforming (APR) of glycerol. It was revealed that, the APR activity of synthesized catalysts strongly depended on the aforementioned ratio. In addition, it was observed that, the catalytic activity of Ni/MgO and Ni/Al2O3 samples were both lower than that of the corresponding mixed oxide supports. Furthermore, it was shown that, amongst the compositionally different prepared mixed oxide materials, the respective catalytic activities increased through enhancing of the Al/Mg ratio. It was demonstrated that the Ni/Al2Mg1 catalyst possessed highest catalytic activity of 92% glycerol conversion and selectivity towards hydrogen production of 76%. Ultimately, it was concluded that, the APR activity lowered in the following order: Ni/Al2Mg1 > Ni/Al1Mg1 > Ni/Al1Mg2 > Ni/Al > Ni/Mg for the understudied synthesized materials.

Hydrogenolysis of glycerol with in-situ produced H2 by aqueous-phase reforming of glycerol using Pt-modified Ir-ReOx/SiO2 catalyst

We found that Pt-modified Ir-ReOx/SiO2 acted as an effective catalyst for aqueous phase reforming (APR) and selective C-O hydrogenolysis of glycerol without external hydrogen sources at low temperature of 463K, and that 0.5wt% loaded Ir-ReOx/SiO2 (Pt(0.5)-Ir-ReOx/SiO2) provided 1,2-propanediol (1,2-PrD) and acetol in high total yield of 53% at 81% conversion. The initial activity (TOFinitial) over Pt(0.5)-Ir-ReOx/SiO2 at 463K was estimated to be 13h−1. Pt-Ir alloy and Ir-ReOx species in Pt-Ir-ReOx/SiO2 are main active species for APR and selective C-O hydrogenolysis, respectively, and the high yield can be achieved by balancing the APR and hydrogenolysis activities through the optimization of Pt and Ir-ReOx molar ratio.

Synthesis of jet fuel rang cycloalkane from isophorone with glycerol as a renewable hydrogen source

For the first time, 1,​1,​3-​trimethyl-cyclohexane (a jet fuel range cycloalkane) was synthesized by coupling the aqueous phase reforming (APR) of glycerol and the hydrodeoxygenation (HDO) of isophorone which can be obtained from lignocellulose. Among the investigated catalysts, Pt/Al2O3 was found to be the most active for the production of 1,​1,​3-​trimethyl-cyclohexane with the hydrogen which was in-situ generated by the APR of glycerol. Over it, high carbon yield (67.0%) of 1,​1,​3-​trimethyl-cyclohexane can be achieved at 533K in the absence of external hydrogen. The excellent performance of Pt/Al2O3 catalyst can be explained because Pt is highly active for both APR and HDO reactions. Besides glycerol, many other lignocellulose derived polylols (such as ethylene glycol, xylitol and sorbitol) and methanol can also be used as renewable hydrogen source for the HDO of isophorone. As a potential application, the 1,​1,​3-​trimethyl-cyclohexane as obtained can be blended into the conventional jet fuels to improve their volumetric heat values.

Performance of Pt and Pt‐Rh catalyst in the hydrogen production from glycerol

AbstractThis paper shows the behaviour of Pt and Pt‐Rh catalysts supported on α‐Al2O3 and γ‐Al2O3 for hydrogen production by glycerol aqueous phase reforming. The catalysts were prepared by wet impregnation with ion exchange correcting the pH of catalysts. The catalyst Pt/α‐Al2O3 showed low activity, high selectivity, and fast deactivation. Its behaviour was completely modified by the presence of Rh, which improved the conversion and the life span. The Pt/γ‐Al2O3 catalyst showed a different behaviour, with more conversion and high life span. The presence of rhodium in this catalyst did not change significantly the catalyst behaviour like other catalysts made with α‐alumina. The yield for hydrogen production was low for all catalysts.

Investigation of the promoting effect of Mn on a Pt/C catalyst for the steam and aqueous phase reforming of glycerol

The catalytic performances in steam reforming (SR) and aqueous phase reforming (APR) of glycerol of a bimetallic Pt-Mn catalyst supported on activated carbon are investigated and correlated with the surface properties of the catalyst. Under SR conditions, Mn showed a significant promoting effect over Pt/C, both in terms of hydrogen production rate and conversion, with a higher selectivity toward the glycerol dehydration products. Upon addition of Mn the amount of strong Lewis acid sites increased, promoting the dehydration of glycerol and favoring the CO over CC cleavage at expenses of hydrogen selectivity. Conversely, under APR conditions, a slightly higher hydrogen selectivity and only minimal enhancement in hydrogen production were found, while the products selectivity was comparable to Pt/C. Most of Mn leached into the aqueous media, but the remaining (<5% of the fresh parent sample) might be alloyed with Pt and promote the CO desorption from neighbor Pt sites.

A DFT and MD study of aqueous-phase dehydrogenation of glycerol on Pt(1 1 1): comparing chemical accuracy versus computational expense in different methods for calculating aqueous-phase system energies

Glycerol, which is one of the most abundant by-products in biodiesel production, can be converted into H2 through aqueous-phase reforming (APR). Dehydrogenation is one of the main processes in glycerol APR. In this work, we use computational methods to study Pt(1 1 1)-catalysed glycerol dehydrogenation under aqueous conditions. There are 84 intermediates and 250 possible reactions in the dehydrogenation network. Inclusion of the liquid environment adds computational expense, especially if we are to study all the reaction intermediates and reactions under explicit water solvation using quantum methods. In this work, we present a method that can be used to efficiently estimate reaction energies under explicit solvation with reasonable accuracy and computational expense. The method couples a linear scaling relationship for obtaining adsorbate binding energies with Lennard-Jones + Coulomb potentials for obtaining water–adsorbate interaction energies. Comparing reaction energies calculated with this approach to reaction energies obtained from a more extensive approach that attains quantum-level accuracy (published previously by our group), we find good correlation (R2 = 0.84) and reasonable accuracy (the mean absolute error, MAE = 0.28 eV).

Aqueous phase reforming of glycerol using doped graphenes as metal-free catalysts

Boron-doped graphene obtained by pyrolysis at 900 °C of the boric acid ester of alginate was found to be the most active graphene among a series of doped and co-doped graphenes to promote the aqueous phase reforming of glycerol at 250 °C.

Optimised hydrogen production by aqueous phase reforming of glycerol on Pt/Al2O3

Aqueous phase reforming of glycerol was studied over a series of γ-Al2O3 supported metal nanoparticle catalysts for hydrogen production in a batch reactor. Of the metals studied, Pt/Al2O3 was found to be the most active catalyst under the conditions tested. A further systematic study on the impact of reaction parameters, including stirring speed, pressure, temperature, and substrate/metal molar ratio, was conducted and the optimum conditions for hydrogen production (and kinetic regime) were determined as 240 °C, 42 bar, 1000 rpm, and substrate/metal molar ratio ≥ 4100 for a 10 wt% glycerol feed. The glycerol conversion and hydrogen yield achieved at these conditions were 18% and 17%, respectively, with negligible CO and CH4 formation. Analysis of the spent catalyst using FTIR provides an indication that the reaction pathway includes glycerol dehydrogenation and dehydration steps in the liquid phase in addition to typical reforming and water gas shift reactions in the gas phase.

Highly selective doped Pt[sbnd]MgO nano-sheets for renewable hydrogen production from APR of glycerol

A series of M-doped PtMgO (M = Pd, Ir, Re, Ru, Rh and Cr) sheet-shaped nano-catalysts were synthesized by the controlled co-precipitation method. The effects of M-doping on both the physicochemical and the chemisorption characteristics of PtMgO catalysts were examined. The performance of the catalysts for the aqueous phase reforming (APR) of glycerol was also investigated. The APR activity of PtMMgO catalysts depended on the type of the M dopant used. The APR activity varied in the following order: Rh > Pd > Cr > Ir > undoped ≈ Ru > Re, with the Rh-promoted catalyst having an activity of about one order of magnitude higher than the Re-promoted catalyst at 250 °C. It was found that M-promotion had a significant effect on the reducibility of the PtMgO catalysts thus affecting their APR activity.

Aqueous phase reforming of glycerol using highly active and stable Pt0.05CexZr0.95-xO2 ternary solid solution catalysts

The aqueous phase reforming (APR) of glycerol is an attractive yet challenging pathway to convert abundant biomass into value added hydrogen. Pt catalysts have received attention due to their ability to produce hydrogen-rich gas under APR conditions. In this work, the conversion of glycerol into hydrogen is demonstrated using Pt0.05CexZr0.95-xO2 (x=0, 0.29, 0.475, 0.66 and 0.95) solid solution catalysts. Both characteristic (XRD, BET, H2-TPR, CO-chemisorption, TEM and XPS) and reactivity measurements were used to investigate the activity of the catalysts. Results indicated that reactivity depended on the Ce/Zr ratio, which in turn affected the Pt oxidation state, active metal dispersion and surface area, and particle size. Among these catalysts Pt0.05Ce0.475Zr0.475O2 showed the highest carbon to gas conversion (95%), highest H2 yield (93%), highest H2 selectivity (98%) and at least 50h of stability. The overall catalytic performance decreased in the order Pt0.05Ce0.475Zr0.475O2>Pt0.05Ce0.29Zr0.66O2>Pt0.05Zr0.95O2>Pt0.05Ce0.66Zr0.29O2>Pt0.05Ce0.95O2.

Effect of biodiesel-derived impurities (acetic acid, methanol and potassium hydroxide) on the aqueous phase reforming of glycerol

This work analyses the influence of three biodiesel-derived impurities (CH3OH, CH3COOH and KOH) on the aqueous phase reforming of glycerol at 220°C and 44bar using a Ni–La/Al2O3 catalyst. The experiments were planed according to a factorial 2k design and analysed by means of an analysis of variance (ANOVA) test to identify the effect of each impurity and all possible binary and ternary combinations. The presence of CH3OH decreased the glycerol conversion, while CH3COOH and KOH decreased and increased the gas production, respectively. Catalyst deactivation took place under acidic conditions due to the loss of part of the active phase of the catalyst through leaching. The gas phase was made up of H2, CO2, CO and CH4. KOH exerted the greatest influence on the gas composition, increasing H2 production due to the greater gas production and the lower H2 consumption in the hydrogenation reactions. The liquid phase was made up of aldehydes, monohydric and polyhydric alcohols, C3 and C4 ketones and esters. CH3OH increased the proportion of monohydric alcohols, while CH3COOH promoted dehydration reactions, leading to an increase in the relative amount of C3-ketones.

Diesel oil-like hydrocarbon production from vegetable oil in a single process over Pt–Ni/Al2O3 and Pd/C combined catalysts

Diesel oil-like hydrocarbon production from vegetable oil (sunflower oil) was addressed in a single process using a catalytic fixed-bed pressure reactor, operating in batch wise under subcritical water conditions without external hydrogen supplied. The process has been decoupled identifying the sequential steps involved in the whole reaction. The non-catalytic hydrolysis of triglycerides to form fatty acids (FFA) and glycerol, the aqueous phase reforming of glycerol and the in situ hydrogenation and deoxygenation of the unsaturated fatty acids are the reactions involved to form diesel oil-like hydrocarbons. Under subcritical water condition, the Pt–Ni/Al2O3 catalyst promotes the glycerol reforming, the complete hydrogenation and the partial deoxygenation of the FFA. The combination of Pt–Ni/Al2O3 and Pd/C catalysts as a double fixed-bed allowed a further decarboxylation of FFA to form a C17-paraffinic hydrocarbon: cetane number of 48.8, density of 0.774g·cm−3 and higher heating value of 47.53MJ·kg−1; comparable to commercial hydrotreated vegetable oil (HVO).

Valorization of Waste Lipids through Hydrothermal Catalytic Conversion to Liquid Hydrocarbon Fuels with in Situ Hydrogen Production

We demonstrate hydrothermal (300 °C, 10 MPa) catalytic conversion of real waste lipids (e.g., waste vegetable oil, sewer trap grease) to liquid hydrocarbon fuels without net need for external chemical inputs (e.g., H2 gas, methanol). A supported bimetallic catalyst (Pt–Re/C; 5 wt % of each metal) previously shown to catalyze both aqueous phase reforming of glycerol (a triacylglyceride lipid hydrolysis coproduct) to H2 gas and conversion of oleic and stearic acid, model unsaturated and saturated fatty acids, to linear alkanes was applied to process real waste lipid feedstocks in water. For reactions conducted with an initially inert headspace gas (N2), waste vegetable oil (WVO) was fully converted into linear hydrocarbons (C15–C17) and other hydrolyzed byproducts within 4.5 h, and H2 gas production was observed. Addition of H2 to the initial reactor headspace accelerated conversion, but net H2 production was still observed, in agreement with results obtained for aqueous mixtures containing model fatty acids and glycerol. Conversion to liquid hydrocarbons with net H2 production was also observed for a range of other waste lipid feedstocks (animal fat residuals, sewer trap grease, dry distiller’s grain oil, coffee oil residual). These findings demonstrate potential for valorization of waste lipids through conversion to hydrocarbons that are more compatible with current petroleum-based liquid fuels than the biodiesel and biogas products of conventional waste lipid processing technologies.

Alumina supported bimetallic Pt–Fe catalysts applied to glycerol hydrogenolysis and aqueous phase reforming

Glycerol hydrogenolysis and aqueous phase reforming (APR) are processes that can transform glycerin into 1,2-propanediol (1,2-PD), ethylene glycol (EG), alcohols, ketones and hydrocarbons. This study was performed using five Ptx–Fey/Al2O3 catalysts in both glycerol hydrogenolysis and APR reactions, with 2.5%wt. metallic Pt total loading and varying Pt:Fe atomic ratios (1:0; 0:1; 2:1; 1:1; 1:2). The catalysts were analyzed by XRD, TPR, XPS, FT-IR, TEM, N2 physisorption and H2 chemisorption, and catalytic tests were undertaken in batch reactions. Except for Fe/Al2O3, all catalysts were active for both APR and hydrogenolysis reactions, in which bimetallic Ptx–Fey/Al2O3 showed better selectivity towards 1,2-PD than Pt/Al2O3. From characterization, it is clear that Pt–Fe interaction displays a pivotal role in enhancing catalytic activity, through the generation of new sites. From the catalytic tests, rate constants and TOF’s were calculated. The addition of Fe had a positive effect both in activity and in selectivity for hydrogenolysis towards 1,2-PD. In APR, there is considerable H2 production, and although activity is greater, there is a slight decline in 1,2-PD production. Through comparison of both reactions’ products, it is evident that some of the hydrogen used in glycerol hydrogenolysis comes from glycerol reforming. Glycerol APR over Ptx–Fey/Al2O3 catalysts seems to be a viable alternative for low temperature H2 production.

Precious Metals Supported on Alumina and Their Application for Catalytic Aqueous Phase Reforming of Glycerol

The high cost of Pt based catalyst for aqueous phase reforming (APR) reaction makes it advantageous to develop less cost of other metals for the same reaction. APR is hydrogen production process from biomass-derived source at mild condition near 500 K and firstly reported by Dumesic and co-worker. The use of hydrogen as environmentally friendly energy carrier has been massively encouraged over the last year. When hydrogen is used in fuel cell for power generation, it produces a little or no pollutants. The aim of this study is to study the effect of some precious metal catalysts for APR process. Due to investigation of metal catalysts for APR process, four precious metals (Cu, Co, Zn, Ni) supported on γ-Al2O3 with 20% feeding amount have been successfully prepared by impregnation method. Those precious metals were identified as promising catalysts for APR. The catalysts were characterized by N2 physisorption at 77 K, X-Ray Diffraction (XRD) and Fourier Transform-Infra Red (FT-IR). The catalytic performance was investigated at 523 K and autogenous pressure in a batch reactor with glycerol concentration of 10%. The gaseous hydrogen product was observed over the prepared catalysts by GC. It was found that performance of catalysts to yield the hydrogen product was summarized as follow Cu/γ-Al2O3 &gt; Co/γ-Al2O3 &gt; Zn/γ-Al2O3 &gt; Ni/γ-Al2O3.

Elucidation of the Roles of Re in Aqueous-Phase Reforming of Glycerol over Pt–Re/C Catalysts

We report the investigation of surface properties of Pt/C and Pt–Re/C catalysts using in situ spectroscopic tools and a fundamental understanding of their catalytic performances in glycerol aqueous-phase reforming (APR). We found that adding Re to Pt/C improves its activity significantly, which is consistent with our previous observation in glycerol steam reforming. However, the difference in reaction selectivity is much more pronounced in APR. Compared to Pt/C, Pt–Re/C yielded significantly more liquid products, while the selectivity to H2 and CO2 decreased by more than 40%. In operando X-ray absorption spectroscopy and attenuated total reflectance infrared (ATR-IR) with in situ capability as well as Raman spectroscopy were employed to investigate the catalyst surface properties and the roles of Re. In operando X-ray absorption fine structure shows significant oxidation of Re, and ATR-IR of adsorbed pyridine revealed the formation of acid sites on PtRe after hot liquid water treatment. Additionally, ATR-IR using CO as a probe molecule demonstrated that desorption of CO from the Pt–Re/C surface is more facile than that from Pt/C in the aqueous phase. We propose that well-dispersed Re oxide species in the proximity of Pt work as the active sites, providing both metal and acid functionalities, while the terminal Re–O moiety has little contribution to the overall reactivity as evidenced by Raman spectroscopy.

Hydrogenolysis of glycerol to propylene glycol by in situ produced hydrogen from aqueous phase reforming of glycerol over SiO2–Al2O3 supported nickel catalyst

In the present work, the reactions of glycerol's aqueous phase reforming (APR) and Aqueous Phase Hydrogenolysis (APH) in a batch reactor containing SiO2–Al2O3 supported 65% Ni catalyst are performed. The effect of: i) the reaction time (30–240min), ii) the operating temperature (200–240°C), iii) the glycerol concentration (1 or 10wt.%), iv) the catalyst weight (0.5–10g) and v) the gas to liquid phase volume ratio (1.4 or 5ml/ml) on: a) the gaseous and liquid product selectivities and b) the glycerol's conversion is investigated. The main gaseous products are found to be H2, CH4 and CO2, while the main liquid products are found to be propylene glycol (PG), ethylene glycol (EG), ethanol and acetol. Glycerol's conversion increases with the reaction evolution and the increase of the temperature, reaching a plateau. It is found that hydrogen yield is maximized at short reaction times, low glycerol concentrations and increased gas to liquid phase volume ratios, reaching up to 23.5%. On the contrary, the PG yield is favored under the inverse conditions, reaching up to 22%. The higher conversion to gaseous products is found to be ~73.6% and the higher conversion to liquid products ~35.6%. It is also found that, the increased catalyst concentration favors the C–C bond cleavage and the formation of ethylene glycol, ethanol and CH4.