Aqueous Phase Reforming Research Articles

Aqueous phase reforming of starch wastewater over Pt and Pt-based bimetallic catalysts for green hydrogen production

This work analyses the application of aqueous phase reforming (APR) for green hydrogen production from starch industry wastewater. This work reports for the first time on the direct conversion of a high molecular weight biomass polymer contained in wastewater in contrast to low molecular weight substrates mainly reported in the literature. The potential of this type of feedstock was evaluated by varying the starch source (rice, potato, sweet potato and cassava) and the type of catalyst (carbon supported Pt, PtRu, PtPd, PtRe and PtRh catalysts). In APR experiments at 220 °C with synthetic wastewater, PtRu/C and Pt/C catalysts achieved the highest H2 yield values, around 51 mmol H2 per g of organic carbon in the initial wastewater, close to 2.6 times higher than that reported in the literature of brewery wastewater, a promising substrate. The lack of free aldehyde or keto groups due to glycosidic bonds between glucose units in starch results in higher conversion to gas and H2 production compared to APR of glucose. This fact shows that APR has more feedstock flexibility than that previously reported for light compounds. In the experiments with real wastewaters, the organic matter removal was influenced largely by the starch source: the best APR performance (28.5 mmol H2 gTOCi−1) was obtained for rice processing wastewater, which is characterized by the highest starch concentration and the lowest protein content. Poor performance was observed in the APR of potato processing wastewater, probably due to catalyst deactivation caused by protein fraction.

Life cycle assessment of the biofuel production from lignocellulosic biomass in a hydrothermal liquefaction – aqueous phase reforming integrated biorefinery

The use of biofuels in the transport sector is one of the strategies for its decarbonization. Here, the LCA methodology was used for the first time to assess the environmental impacts of a biorefinery where hydrothermal liquefaction (HTL) and aqueous phase reforming (APR) were integrated. This novel coupling was proposed to valorize the carbon loss in the HTL-derived aqueous phase, while simultaneously reducing the external H2 demand during biocrude upgrading. Corn stover (residue) and lignin-rich stream (waste) were evaluated as possible lignocellulosic feedstocks. The global warming potential (GWP) was 56.1 and 58.4 g CO2 eq/MJbiofuel, respectively. Most of the GWP was attributable to the electrolysis step in the lignin-rich stream case and to the thermal duty and platinum use in the corn stover case. Other impact categories were investigated, and an uncertainty analysis was also carried out. A sensitivity analysis on biogenic carbon, electricity/thermal energy source and alternative hydrogen supply was conducted to estimate their influence on the GWP. Finally, the two scenarios were compared with the environmental impact of fossil- and other biomass-derived fuels, also considering fuel utilization. HTL-APR allowed a 37% reduction compared to fossil diesel, further reduced to 80% with the lignin-rich stream when green energy was used.

Low-temperature upcycling of PET waste into high-purity H2 fuel in a one-pot hydrothermal system with in situ CO2 capture.

The accumulation and improper disposal of a large amount of plastic waste have exacerbated the deterioration of the global ecosystem and environment. To simplify the complex management system and alleviate the environmental impact of plastic wastes, this study reports a novel one-pot hydrothermal conversion strategy for polyethylene terephthalate (PET), integrating three steps, namely depolymerization, subsequent in-situ aqueous phase reforming, and in-situ CO2 capture. Here, the PET waste was converted directly into the clean high-purity H2 fuel and the disodium terephthalate (Na2-TPA). A high yield of H2 at 23.7mol/kgPET with ca. 99 % of H2 concentration was obtained at a temperature as low as 240°C. The feasibility of this strategy in handling real-world PET plastic wastes was demonstrated through a series of tests on beverage bottles, food packaging, and polyester fabric waste. The Na2-TPA crystals produced from the proposed PET conversion system exhibited purity close to that of the standard sample, and thus had the potential to be directly used as an electrode material. Overall, this strategy provides an efficient way to transform PET waste into high-value products and improves the sustainability of the PET waste disposal process.

Improving the hydrothermal stability and hydrogen selectivity of Ni-Cu based catalysts for the aqueous-phase reforming of methanol

Non-precious metal catalysts suitable for hydrogen production via aqueous phase reforming (APR) of methanol show important technical and commercial value in the development of distributed, small/micro-scale on-site hydrogen production systems. They still face the challenges of reduced activity and stability due to sintering and oxidation of active metal nanoparticles, change of the surface state and collapse of the pore structure of used supports under hydrothermal conditions. To solve these problems, a series of ZnO/Ni-xCu/Al2O3 (x = 0, 2, 4, 6, 8, 10) catalysts were prepared by a simple impregnation method in this work. The addition of Cu improved the reducibility of NiO, and promoted the formation of smaller and more dispersed metal particles on the surface of Al2O3, facilitating hydrogen production and hindering methane formation. Among them, the highest average hydrogen production rate (362.1 μmol‧min−1‧gcat−1) and the highest hydrogen selectivity (99%) were reached using ZnO/Ni-8Cu/Al2O3 catalyst, which were 1.6 times and 20.7% higher than those obtained on the mono-metallic ZnO/Ni/Al2O3 catalyst, respectively. On the other hand, the modification of Ni-8Cu/Al2O3 with ZnO prevented effectively the reaction of surface water with Al2O3 and inhibited the formation of boehmite phase, leading to dramatical improvement of its stability during APR of methanol with a prolonged lifetime (72 h) by 6 times. This new developed ZnO/Ni-xCu/Al2O3 catalysts offer great potential for the development of commercial catalysts to produce hydrogen from APR of methanol.

Hydrogen production via the aqueous-phase reforming of methanol catalyzed by Ru(ii) complexes of PNNP ligands

Hydrogen production by the aqueous-phase reforming of methanol has attracted much interest as it offers a convenient means of producing H2 on demand by mitigating the costs and safety challenges associated with the storage and transportation of H2.

CeO2-supported Ni and Co catalysts prepared by a solution combustion method for H2 production from glycerol: the effect of fuel/oxidizer ratio and oxygen excess

The impact of the fuel/oxidizer ratio, the fuel type and the oxygen excess in the synthesis of ceria supported Ni and Co catalysts on the physicochemical properties and activity in steam and aqueous-phase reforming of glycerol was studied.

Efficient H2 Production from PET Plastic Wastes over Mesoporous Carbon-Supported Ru-ZnO Catalysts in a Mild Pure-Water System

The massive consumption of plastic is posing severe pollution-related challenges globally. As the most abundant polyester plastic, polyethylene terephthalate (PET) waste represents a largely untapped resource for generating chemicals and fuels. However, the current widespread use of alkali/organic solvents and the complex processing of PET reduce its environmental sustainability. Herein, a novel and simple one-pot strategy was first reported for the catalytic conversion of PET into H2 fuel and terephthalic acid in a pure-water system under mild conditions. A high H2 yield of 19.97 mol/kgPET and carbon conversion efficiency of 97.22% were obtained for the Ru-5ZnO/mesoporous carbon (MEC) catalyst at a low temperature of 250 °C. This process proceeds through tandem catalytic reactions with an initial PET depolymerization step, followed by in situ aqueous phase reforming (APR) of ethylene glycol of Ru. Remarkably, ZnO inhibited the deactivation of Ru/MEC in the PET depolymerization stage, causing an increase in H2 production from the in situ APR stage. Importantly, this strategy was successfully applied to four types of real-world PET waste and their mixtures, demonstrating that it has considerable potential in practical applications and provides a sustainable and clean solution to the plastic waste problem.

Bio‑hydrogen and valuable chemicals from industrial waste glycerol via catalytic aqueous-phase transformation

Waste glycerol obtained as by-product of biodiesel production has been submitted to a sequential physico-chemical treatment in order to make it suitable for continuous Aqueous-Phase Reforming (APR) in a tubular reactor. Special focus was given to the impact of impurities. APR was performed using 0.3%Pt/CoAl2O4 catalyst, at 260 °C and 50 bar within WHSV range 6–55 h−1 to cover whole conversion ranges. Glycerol conversion and yield to hydrogen reached 99.7% and 45.4%, respectively at WHSV = 6 h−1. The liquid product distribution strongly varied with glycerol conversion, maximum C-yield to 1,2-propylene glycol was attained in the 60–90% glycerol conversion range. APR of methanol and acetic acid aqueous feedstreams were investigated independently. It was concluded that acetic acid exerts a negative influence on catalyst stability since glycerol conversion decreased by 41% after 5 h TOS. Extensive characterization of fresh and exhausted catalysts revealed strong Co leaching, especially for acetic acid APR, oxidation of metals, and carbonaceous deposits. The basis for the regeneration of the spent catalyst, consisting of a reductive treatment at 500 °C, has been established. This work is expected to have significant implications for the development of APR technology for crude glycerol from biodiesel industry.

Sorption enhanced aqueous phase reforming of biodiesel byproduct glycerol for hydrogen production over Cu-Ni bimetallic catalysts supported on gelatinous MgO

Hydrogen production from sorption enhanced aqueous phase reforming (APR) of biodiesel byproduct glycerol was studied by Ni-based monometallic and bimetallic catalysts supported on gelatinous MgO supports. Compared with Ni-based monometallic catalyst, the H2 selectivity and glycerol conversion of the Cu–Ni bimetallic catalyst were found to be increased more than 3% and 30%, respectively. Meanwhile, higher reaction temperature was found to have higher H2 yield with lower H2 selectivity. The H2 yield using the catalyst with gelatinous MgO support was 1.25 times higher than that of calcined support. Through in-situ CO2 capture, the addition of CaO to the Cu–Ni bimetallic catalyst increased more than 58.3% and 14.4% of the H2 yield and selectivity, respectively. An analysis about liquid product component indicate that the presence of CaO promote the further cleavage of the C–C bond, which further increased the conversion of glycerol. Furthermore, it was found that the presence of CaO could also improve the stability of the catalyst through the control experiments.

Conceptual design and techno-economic assessment of coupled hydrothermal liquefaction and aqueous phase reforming of lignocellulosic residues

Hydrothermal liquefaction is a promising technology for producing renewable advanced biofuels. However, some weaknesses could undermine its large-scale application, such as the significant carbon loss in the aqueous phase (AP) and the necessity of biocrude upgrading. In order to deal with these challenges, in this work the techno-economic feasibility of coupling hydrothermal liquefaction (HTL) with aqueous phase reforming (APR) was evaluated. APR is a catalytic process able to convert water-dissolved oxygenates into a hydrogen-rich gas that can be used for biocrude upgrading. Two cases were proposed, based on different lignocellulosic feedstocks: corn stover (CS) and lignin-rich stream (LRS) from cellulosic ethanol production. HTL-APR plants operating with the same mass flow (3.6 t/h) at 10 wt% solid loading were herein evaluated, resulting in an input size of 20 MW (LRS) and 16.5 MW (CS). Based on experimental and literature data, the mass and energy balances were performed; subsequently, the main equipment was designed; finally, the capital and operating costs were evaluated. The analysis showed that the minimum selling prices for the biofuel (0% internal rate of return) were 1.23 (LRS) and 1.27 €/kg (CS). The heat exchangers accounted for most of the fixed capital investment, while electricity and feedstock had the highest impact on the operating costs. The implementation of APR was particularly profitable with CS, as it produced 107% of the hydrogen required for biocrude upgrading. In this case, APR was able to significantly reduce the H2 production cost (1.5 €/kg) making it a competitive technology compared to conventional electrolysis.

Metal-carbonate interface promoted activity of Ag/MgCO3 catalyst for aqueous-phase formaldehyde reforming into hydrogen

Aqueous-phase reforming of biomass-derived formaldehyde is one of efficient and sustainable routes to generate molecular hydrogen as clean energy resource. In this work, Ag/MgCO3 catalyst is prepared with constructed stable carbonate-modified metal-support interfaces. Under mild and neutral reaction conditions, it exhibits a near an order of magnitude higher low-temperature activity in formaldehyde reforming reaction for producing hydrogen in comparison with Ag/MgO. The catalytic and spectral observations reveal that the Ag/MgCO3-catalyzed reaction follows an O2-involved HCHO/H2O reforming reaction pathway through O2−, OOH and H radicals as highly active intermediates. Ag/MgCO3 catalyst shows high rates in isotopic H2-D2 exchange and HCHO/D2O reforming reactions and displays an apparent activation energy (Ea) as low as 7.5 kJ mol−1 within 10–50 °C, indicating facile activation of HCHO CH and H2O OH bonds. Furthermore, Ag/MgCO3 catalyst adsorbs HCHO molecule in a favorable configuration and strength, as evidenced by the HCHO desorption profile. Comprehensive positive factors benefit to the superior hydrogen production activity of carbonate-modified Ag/MgCO3 than Ag/MgO.

The influence of phase purity on the stability of Pt/LaAlO3 catalysts in the aqueous phase reforming of glycerol

Aqueous phase reforming (APR) of waste oxygenates offers the potential for sustainable hydrogen production. However, catalyst stability remains elusive, due to the aggressive hydrothermal conditions employed. Herein, we show that the catalytic performance and stability of Pt supported on LaAlO3 catalysts for glycerol APR is strongly influenced by the phase purity of LaAlO3. Calcination of the support at 700 °C produces the LaAlO3 perovskite phase and an amorphous lanthanum carbonate phase, which can be removed by calcination at higher temperature. Catalysts comprised of phase pure LaAlO3 were notably more active, with a support calcination temperature of 1100 °C resulting in 20.4% glycerol conversion (TOF 686 h−1) in a 2 h batch reaction. Interestingly, all the catalysts, regardless of LaAlO3 phase purity, eventually transform into Pt/LaCO3OH-AlO(OH) during reaction, but only in the presence of evolved carbon dioxide, itself produced from glycerol reforming. Studies using simulated reaction products showed that organic acid products (lactic acid), in the absence of CO2, facilitated La leaching and loss of crystallinity. A carbonate source (CO2) is essential to limit La leaching and form stable Pt/LaCO3OH. Pt supported on LaCO3OH and AlO(OH) are stable and active catalysts during APR reactions. Yet, the rate of perovskite phase decomposition strongly influences the final catalyst performance, with the initially phase impure LaAlO3 decomposing too quickly to facilitate Pt redistribution. LaAlO3 calcined at higher temperatures evolved more slowly and consequently produced more active catalysts.

Toward Sustainability of the Aqueous Phase Reforming of Wastewater: Heat Recovery and Integration

Aqueous-phase reforming has been revealed as a novel, interesting and efficient process for the treatment of wastewater containing organic pollutants. However, due to the relatively severe operating conditions (above 15 bar and 200 °C), this process could become economically competitive if any solution for energy or material valorization is implemented. Most research has been devoted to direct the process to H2 production as an alternative to reach economic sustainability, but the results obtained were not competitive in the current market of hydrogen and syngas. In this work, a preliminary simulation study (using Aspen HYSYS software) of the process heat balance in different conditions was implemented to induce a heat integration that would allow the auto-sustainability of the process, even generating in some cases an excess of energy that could constitute an opportunity for a positive economic balance. The results showed that this approach would only be possible by maximizing the methane production to the detriment of hydrogen production.

Aqueous-phase reforming of water-soluble compounds from pyrolysis bio-oils

Aqueous-phase reforming (APR) of model compounds of bio-oil aqueous fraction (AFB) was studied at different operating conditions. Substrate conversion, carbon-to-gas yield (CCgas) and hydrogen and alkanes production were evaluated. Levoglucosan, hydroxyacetone, furfural and acetic acid were selected as representative of AFB and tested in batch APR at different concentrations (1–5 %wt.), temperatures (175–220 °C) and reaction times (0.5–4 h), using 3% (wt.) Pt/CB catalysts. Best results were obtained at 220 °C and 1%, with 70–90% substrate conversions, 45–70% CC gas and hydrogen production up to 50 mmol per gram of total organic carbon (TOC). Catalyst stability was checked in APR of levoglucosan during five successive 4 h reaction cycles. The catalyst exhibited high stability, CCgas remained constant and hydrogen production increased and became stable after first reaction cycle with only a slight decrease of TOC conversion. The catalyst with well dispersed metal phase and high contribution of nanoparticles smaller than 2 nm showed a higher production of hydrogen. APR was proved to be a feasible option for the valorisation of AFB.

Aqueous-phase reforming of hydroxyacetone solution to bio-based H2 over supported Pt catalysts

Aqueous-phase reforming (APR) is an attractive process to produce bio-based hydrogen from waste biomass streams, during which the catalyst stability is often challenged due to the harsh reaction conditions. In this work, three Pt-based catalysts supported on C, AlO(OH), and ZrO2 were investigated for the APR of hydroxyacetone solution in a fixed bed reactor at 225 °C and 35 bar. Among them, the Pt/C catalyst showed the highest turnover frequency for H2 production (TOF of 8.9 molH2 molPt−1 min−1) and the longest catalyst stability. Over the AlO(OH) and ZrO2 supported Pt catalysts, the side reactions consuming H2, formation of coke, and Pt sintering result in a low H2 production and the fast catalyst deactivation. The proposed reaction pathways suggest that a promising APR catalyst should reform all oxygenates in the aqueous phase, minimize the hydrogenation of the oxygenates, maximize the WGS reaction, and inhibit the condensation and coking reactions for maximizing the hydrogen yield and a stable catalytic performance.

Production of Propanediols through In Situ Glycerol Hydrogenolysis via Aqueous Phase Reforming: A Review

Production of 1,2-propanediol and 1,3-propanediol are identified as methods to reduce glycerol oversupply. Hence, glycerol hydrogenolysis is identified as a thermochemical conversion substitute; however, it requires an expensive, high-pressure pure hydrogen supply. Studies have been performed on other potential thermochemical conversion processes whereby aqueous phase reforming has been identified as an excellent substitute for the conversion process due to its low temperature requirement and high H2 yields, factors which permit the process of in-situ glycerol hydrogenolysis which requires no external H2 supply. Hence, this manuscript emphasizes delving into the possibilities of this concept to produce 1,2-propanediol and 1,3-propanediol without “breaking the bank” with expenses. Various heterogenous catalysts of aqueous phase reforming (APR) and glycerol hydrogenolysis were identified, whereby the combination of a noble metal, support, and dopant with a good amount of Brønsted acid sites are identified as the key factors to ensure a high yield of 1,3-propanediol. However, for 1,2-propanediol, a Cu-based catalyst with decent basic support is observed to be the key for good yield and selectivity of product. The findings have shown that it is possible to produce high yields of both 1,2-propanediol and 1,3-propanediol via aqueous phase reforming, specifically 1,2-propanediol, for which some of the findings achieve better selectivity compared to direct glycerol hydrogenolysis to 1,2-propanediol. This is not the case for 1,3-propanediol, for which further studies need to be conducted to evaluate its feasibility.

The Critical Role of Phenolics on Gasification of Biomass Hydrolysate

The study was designed to solubilize sorghum by water extraction and investigate the effect of phenolics depending on the time in sorghum hydrolysate for hydrogen gas production by aqueous-phase reforming. The Folin-Ciocalteau method was used to determine the total water soluble phenolics of the sorghum hydrolysate. There were no significant changes in the total amount of phenolic compounds during the first weeks. It was observed that the total amount of water soluble phenolic compounds of sorghum hydrolysates showed changes monthly (300-400 ppm). The gas volume produced reached up to 40-50 mL was obtained when the hydrolysates were gasified. APR of biomass hydrolysates in the presence of a reforming catalyst (Pt 5% on activated carbon) produced various amount of gas mixture which consisted of H2, CH4 and CO2 gases. The results showed that the decrease in total water soluble phenolics of sorghum hydrolysate had no significant effect on gasification, depending on the time.

Promoting mechanism of alkali for aqueous phase reforming of bio-methanol towards highly efficient production of COx-free hydrogen

Transforming the poisonous CO generated on the active metal sites promptly is essential for Ni-based catalyst applying in aqueous-phase reforming (APR) of biomass-derived oxygenated hydrocarbons, e.g. methanol, due to its low water-gas-shift (WGS) activity. Here, we used alkali modifier in the APR of methanol (APRM) with a Ni@NC catalyst and explored the promotion mechanism of alkali in depth. Compared with the performance of APRM over the Ni@NC catalyst without using any alkali, the hydrogen production rate increased to 8 times higher (from 33.4 to 265.4 μmolH2/gcat./s), while the CO selectivity decreased drastically (from 26.8% to 0.1%) after adding KOH at 220 °C. Through IR and XRD analysis of the produced potassium salts, it was found that the KOH mainly directly reacted with the CO produced from methanol dehydrogenation forming HCOOK, which eliminated the poisonous effect of CO on the active Ni sites and promoted methanol dehydrogenation remarkably. Besides, a small amount of KOH reacted with CO2 and promoted the WGS, by which in situ stabilization of CO2 was realized, reducing carbon emission. As a result, COx-free hydrogen at a high production rate was achieved, with HCOOK, the precursor for the important hydrogen carrier formic acid, as a side product.

Novel Pt/MoS2 nanosheet catalyst for hydrogen production via aqueous-phase reforming of methanol

Novel Pt/MoS2 nanosheet catalyst for hydrogen production via aqueous-phase reforming of methanol

Hydrothermal oxygen uncoupling of high-concentration biogas slurry over Cu-α-Fe2O3·α-MoO3 catalyst

A hydrothermal oxygen uncoupling (HTOU) method which combines aqueous phase reforming (APR) and oxygen uncoupling was proposed to treat biogas slurry (BS). Based on Le Chatelier's principle, this novel approach was constructed and realized by Cu–α-Fe2O3·α-MoO3 catalyst with van der Waals heterojunction-redox property. Additionally, the catalyst was synthesized by integrating a simple one-pot sol-gel method and thermal hydrogenating. Results indicated that the optimal removal efficiencies of non-purgeable organic carbon (NPOC) (76.29%), total nitrogen (TN) (45.56%), and ammonia nitrogen (AN) (29.03%) were achieved on the Cu–α-Fe2O3·α-MoO3 catalyst at 225.00 °C for 30.00 min, respectively. The significant performance of Cu–α-Fe2O3·α-MoO3 could be attributed to three aspects. (1) The α-MoO3 nanosheets with van der Waals heterostructures obtained at the calcination temperature of 600.00 °C, which can provide the superior performance of APR for hydrogen generation. (2) The adsorbed oxygen species were eliminated by thermal hydrogenating which had a surface passivation effect. (3) The effect of oxygen uncoupling in the lattice oxygen and gaseous oxygen release reaction was beneficial to the degradation of organic matter. Moreover, the reuse of catalysts studies further revealed that the deactivation of catalysts originated from carbon deposition of aromatic polymers and heavy metals oxides pollution. Overall, these findings disclosed that the HTOU could be a promising alternative to the treatment of high-concentration organic wastewater.