Catalysts For Aqueous-phase Reforming Research Articles

Influence of calcination temperature on the evolution of α-MoO3 nanosheets catalyst for aqueous phase reforming of biogas slurry

Renewable hydrogen sources from organic wastewater, which is increasingly recognized as one of the key strategies to achieve carbon peaking and carbon neutrality goals under the new development philosophy. Meanwhile, the treatment of biogas slurry (BS) has a serious impact on the environment, hindering the application of anaerobic digestion. In this study, a novel method that combined aqueous phase reforming (APR) over α-MoO3 nanosheets and activated carbon adsorption was presented, considering sustainable management and conservation of resources. This study examined the relationships between catalyst calcination temperature and catalytic performance of α-MoO3 nanosheets in the APR of BS. A series of catalysts synthesized by thermally hydrogenating and calcined from 400 to 700 °C were characterized and evaluated. Results indicated that hydrogen yield increased at first and then decreased with the increment of calcination temperature due to the change of van der Waals (vdW) heterostructures. The shrinkage of vdW heterostructures of α-MoO3 nanosheets can contribute to the generation of hydrogen because of the low oxygen vacancies and surface acidic property. As a result, the optimal removal efficiencies of the pollutants (non-purgeable organic carbon (NPOC), chemical oxygen demand (COD), total nitrogen (TN), and ammonia nitrogen (AN)) reached 79.45%, 87.82%, 49.78%, and 50.22%, respectively. The optimal hydrogen yield (4.91 mLHydrogen/mLBS) was also achieved using α-MoO3 nanosheets calcined at 600 °C. This work can provide an effective strategy to treat and utilize organic wastewater.

Nitrogen-containing carbon nanofibers as supports for bimetallic Pt-Mn catalysts in aqueous phase reforming of ethylene glycol

Aqueous phase reforming (APR) of ethylene glycol was performed at 225 °C and 30 bar in batch and continuous reaction conditions. The effect on the APR performance by functionalizing carbon supports with nitrogen and adding Mn to Pt-based catalysts was investigated. The presence of nitrogen species on the carbon surface and Mn-addition (PtMn) improved the catalytic activity and promoted H2 production. XPS results suggest that the enhancement of the catalytic activity may be attributed to charge transfer from platinum to the nitrogen groups and Mn. Pt-based catalysts were stable under the studied reaction conditions, while up to 97 % of the manganese leached into the liquid solution during APR. However, the catalytic activity was maintained even with such significant decrease in Mn content, indicating that only a small amount of Mn is necessary to maintain the promotional effect on Pt during APR.

Identifying the realistic catalyst for aqueous phase reforming of methanol over Pt supported by lanthanum nickel perovskite catalyst

In-situ supply of H2 by aqueous phase reforming (APR) of methanol is promising but still challenging due to the unsatisfied activity and stability of catalyst. Herein, we prepared lanthanum nickel perovskite supporting Pt catalysts and evaluated their performance in methanol APR. A transformation from lanthanum nickel perovskite into LaCO3OH happened after APR. The characterizations results reveal that these two perovskite catalysts transformed into LaCO3OH supporting Pt and NiOx structure. We further prepared Pt-NiOx/LaCO3OH catalyst to verify it. Combining with temperature programmed surface reaction, a possible mechanism is proposed. The transformed catalyst possessed more metallic Pt sites and more abundant active OH groups, which are beneficial for methanol decomposition and CO shift, respectively. In addition, although the structure transformation happened for perovskite supporting Pt catalyst, it presented extremely excellent stability with only 7% loss of its highest rate of hydrogen production after 315 h on stream.

Comparison of gelatinous and calcined magnesia supported Ni or/and Co-based catalysts for aqueous phase reforming of glycerol

In this work, two different types of catalysts with MgO support for aqueous phase reforming of glycerol were prepared by the sol-gel method and calcining method, respectively, and the active metals (nickel or/and cobalt) were added by the initial wet impregnation (IWI) method. It is found that the catalyst supported by gelatinous MgO presents better dispersion and the amount of hydrogen produced by the catalyst containing gelatinous MgO support is more than 1.5 times compared with other catalysts. For the Ni–Co bimetallic catalysts, the higher reaction temperature is beneficial to hydrogen yield, but decreases hydrogen selectivity. A high concentration of glycerol increases hydrogen yield and selectivity. Introducing CaO as an absorbent in aqueous phase reforming can improve WGS reaction and reduce methanation reaction through in-situ CO2 removal and capture. The gelatinous Ni–Co/MgO catalyst presents superior activity and multi-cycle stability.

A highly active and hydrothermal-resistant Cu/ZnO@NC catalyst for aqueous phase reforming of methanol to hydrogen

Aqueous-phase reforming (APR) of methanol provides a safe way to store and transport hydrogen by in situ production of H2. It remains, however, a challenge to develop an efficient and hydrothermal-stable non-noble-metal catalyst. Herein, a robust Cu/ZnO@NC catalyst is successfully constructed by encapsulating Cu/ZnO species in nitrogen-doped carbon (NC), using ZIF-8 as precursor. It is demonstrated that the activity for APR of methanol increases exponentially with rise of catalyst wettability. With good wettability, a high hydrogen releasing rate of 146.9 μmol·gcat−1·s−1 is achieved on the 27%Cu/ZnO@NC catalyst at 230 °C, about four times higher than that of a traditional 29%Cu/ZnO catalyst, and surprisingly comparable to a commercial Pt/C catalyst. Notably, Cu/ZnO@NC also shows excellent stability, as the NC coating protects ZnO from hydrolyzing and prevents aggregation of Cu nanoparticle largely in the severe aqueous-phase-reaction conditions. This work develops a convenient method to prepare efficient and hydrothermal-stable catalyst with commercial potential.

Citric acid modified Ni3P as a catalyst for aqueous phase reforming and hydrogenolysis of glycerol to 1,2-PDO

The addition of citric acid reduced the Ni3P particle size, leading to high performance in glycerol hydrogenolysis without external H2.

Highly stable Pt/CoAl2O4 catalysts in Aqueous-Phase Reforming of glycerol

Pt/CoAl2O4 catalysts with small amounts of Pt (0.3 and 1 wt.%) were prepared by wet impregnation of platinum on cobalt aluminate (mole ratio Co/Al = 0.625). These catalysts were compared with monometallic Pt/alumina and cobalt aluminate counterparts. The physicochemical characteristics of the obtained materials were thoroughly analysed. The catalytic performance of the prepared assays was investigated in the Aqueous-Phase Reforming (APR) of glycerol for up to 100 h TOS, and in liquid phase Water-Gas Shift (WGS). It was concluded that the addition of Pt to cobalt aluminate resulted in a synergistic effect that promoted the reduction of both Pt and Co species, as well as cobalt dispersion, what increased the amount of exposed metallic sites. These effects were, however, sensitive to the amount of Pt loaded. The glycerol APR activity of bimetallic catalysts was very stable over 100 h TOS with conversion values above 99 %. Conversion to gas was also above 95 % during the whole operation. Contrarily, the counterpart monometallic catalysts suffered noticeable deactivation at above 70 h TOS. Also, WGS activity of bimetallic assays was higher than the monometallic counterparts. Addition of Pt to cobalt aluminate lowered selectivity to hydrogen, due to a higher CO hydrogenation activity. Examination of the spent catalysts showed better textural stability of the bimetallic samples, as well as much lesser formation of carbonaceous surface deposits. Nevertheless, oxidation and leaching of cobalt remains as the main drawback of bimetallic catalysts to be used in APR.

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.

Graphene as Metal‐Free Catalyst for Aqueous Phase Reforming of Ethylene Glycol

AbstractGraphene obtained by pyrolysis of alginate shows in the absence of any metal, catalytic activity towards the decomposition of ethylene glycol into hydrogen and carbon dioxide at 250 °C due to the presence of hydrogenating/dehydrogenating sites. This reaction has interest in the context of valorization of waste waters from cellulose depolymerization and it is typically catalyzed by platinum and other transition metals. In this regard, the use of graphene as metal‐free catalyst may have a considerable advantage from the point of sustainability of the catalyst. Based on the influence of the presence of acids and bases and the lack of influence of quenchers of reactive oxygen species, it is proposed that the active sites on the graphene could be frustrated acid‐base Lewis pairs acting as dehydrogenating centers. Controls with oxalic acid and glyoxal have shown that if ethylene glycol is converted into these α‐dicarbonylic compounds, spontaneous decarboxylation would occur totally (oxalic acid) or in some extent (glyoxal. 30%). In the last case, decarboxylation is also assisted by graphene.

Hydrothermal stability improvement of NiPt-containing γ-Al2O3 catalysts tested in aqueous phase reforming of glycerol/water mixture for H2 production

The hydrothermal stability of Ni and NiPt-containing γ-Al2O3 catalysts in aqueous phase reforming (APR) of glycerol/water mixture (C3H8O3/H2O, 10% w/w) was investigated putting in evidence the influence of the preparation method; sol–gel in basic medium (SGB) and impregnation on an in-house prepared sol–gel γ-Al2O3 support (SGI). All developed catalysts were characterized by ICP-AES, TPR-H2, in-situ heating XRD-O2, DSC/TG-N2/O2 and ex-situ reduction of XRD-H2, N2 physisoption and TEM techniques. The results indicate that SGI method and calcination treatment at 750 °C were crucial in extending the catalytic useful life of NiPt-containing γ-Al2O3 catalysts, resulting in an adequate distribution of NiPt metallic particles and good stability of γ-Al2O3 support against the severe hydrothermal conditions of APR process. The SGI method led to form stable NiPt catalysts with relatively big Ni particles and stable hydrothermal properties of γ-Al2O3 support, while the SGB catalysts exhibited well-dispersed Ni particles but unstable catalytic behavior. These last catalysts presented high glycerol conversions during the first hours of APR glycerol/water reaction, however, an important decrease in terms of glycerol conversion was observed after 24 h time-on-stream. The experimental results suggested that the most suitable stable and active catalyst was the NiPt/ASGI7 (better than >NiPt/ASGI6 > NiPt/ASGI5 >>> NiPt/ASGB7). This catalyst showed best catalytic activity and good catalytic stability along 56 h of time-on-stream, reaching, at steady state, highest total glycerol conversion (≈79%) and glycerol into gaseous products (≈57%) in APR reaction of glycerol/water mixture for hydrogen generation.

Formation of Ru active species by ion-exchange method for aqueous phase reforming of acetic acid

NaY-zeolite was employed as a support of ruthenium catalysts for aqueous phase reforming of acetic acid. Catalytic activities of the supported ruthenium species on NaY-zeolite depended on oxidation state controlled by preparation conditions. Catalyst NaY(exc), whose 5 wt% ruthenium precursors were supported through cation-exchanging process, produced H2 continuously for 10 h when the catalysts were used without reducing by H2 prior to usage. Decreasing the loading amounts of ruthenium on NaY(exc) led to improve the selectivity toward complete reforming of acetic acid giving H2 and CO2 because of the strong interaction between positively charged ruthenium particle and the support. However, contents of sodium cations controlled by the pH of precursor solutions did not affect the catalytic performances.

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 > Co/γ-Al2O3 > Zn/γ-Al2O3 > Ni/γ-Al2O3.

Toward stable nickel catalysts for aqueous phase reforming of biomass-derived feedstock under reducing and alkaline conditions

Nickel nanoparticles supported on carbon nanofibers (CNF) can be stabilized in aqueous phase processes at elevated temperatures and pressures by tuning the reaction conditions to control Ni oxidation and leaching. As a showcase, Ni/CNF was used for the production of hydrogen via aqueous phase reforming of ethylene glycol (EG). Under standard conditions (T=230°C, inert atmosphere, 1wt.% EG), extensive catalyst deactivation occurred as a result of Ni particle growth. The extent of Ni particle growth was diminished either by using a more reducing environment by introducing additional H2 into the reactor or by increasing the concentration of reactant. Deactivation of the Ni/CNF catalyst due to particle growth was almost completely prevented by addition of KOH to the reaction mixture. Stable H2 production was achieved with high hydrogen selectivity (99%) during 50h on stream by addition of KOH, while without KOH the catalyst lost 93% of its initial activity and the H2 selectivity was lower (90%). The increased stability of Ni particles under both alkaline and reducing conditions is ascribed to the suppression of Ni leaching, which prevented subsequent particle growth via Ostwald ripening.

Linking Performance with Particle Configuration on Bimetallic Pt/Co/MWCNT Catalysts for Aqueous Phase Reforming by Aberration Corrected STEM coupled with EELS

Linking Performance with Particle Configuration on Bimetallic Pt/Co/MWCNT Catalysts for Aqueous Phase Reforming by Aberration Corrected STEM coupled with EELS

Pt-Re synergy in aqueous-phase reforming of glycerol and the water–gas shift reaction

The synergy between Pt and Re in aqueous-phase reforming (APR) of glycerol and the water–gas shift (WGS) reaction was investigated for a series of carbon-supported Pt, Re, and PtRe catalysts. The overall activity of the bimetallic catalysts in APR of glycerol increases with Re content. The ratio of products obtained via C–O bond cleavage to those obtained by C–C bond cleavage also increases with Re content. H2-TPR studies and EXAFS show that Pt and PtRe catalysts are well reduced and remain so during gas- and aqueous-phase reactions. PtRe catalysts are substantially more active in C–C bond cleavage (acetaldehyde decomposition) than their monometallic counterparts, although there is no strong dependence on the Pt/Re ratio. Higher dehydration rates for PtRe alloys correlate with the increasing concentration of steam-treating-induced Brønsted acidic sites (NH3 TPD and FTIR of adsorbed pyridine). The higher glycerol conversion rate of PtRe catalysts compared to Pt mainly stems from the higher rate of CO removal from the surface by the WGS reaction. Pt and Re exhibit a very strong synergy in the gas-phase WGS reaction. Consistent with this, CO stripping voltammetry points to lower onset of CO electro-oxidation for PtRe than for Pt. It is argued that the main influence of Re is its stronger binding of oxygen species facilitating water activation, producing OH species which are involved in the WGS reaction and in C–O bond cleavage reactions.

Catalytic properties of Pt/Al2O3 catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al2O3 catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H2PtCl6. The highest rate of hydrogen production (452 μmol min−1 g−1) obtained with the Pt/α-Al2O3 catalyst can be related to the highest extent of dispersion of Pt on α-Al2O3. XPS, TEM-EDX and TPR-H2 measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al2O3 catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al2O3 and Pr/δ-Al2O3 catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.

Aqueous-phase reforming of ethylene glycol to hydrogen on Pd/Fe 3O 4 catalyst prepared by co-precipitation: Metal–support interaction and excellent intrinsic activity

A high-performance Pd/Fe 3O 4 catalyst for aqueous-phase reforming (APR) of ethylene glycol (EG) to H 2 was prepared facilely by the co-precipitation method. After proper activation, the Pd was present as highly dispersed metallic nanoparticles with dimension of <3 nm, and the Fe was present as magnetite. When compared to Pd catalyst supported on Fe 2O 3, NiO, Cr 2O 3, Al 2O 3, or ZrO 2 prepared by incipient wetness impregnation, the Pd/Fe 3O 4 catalyst displayed superior catalytic performance in terms of activity, selectivity, and stability. The intrinsic activity of the Pd/Fe 3O 4 catalyst was about three times of that of the second most active Pd/Fe 2O 3 catalyst under the same reaction conditions. In addition, the Pd/Fe 3O 4 catalyst retained ∼80% of its initial activity after reaching the steady-state. Notably, the Pd/Fe 3O 4 catalyst possessed the highest turnover frequency of H 2 (109 min −1) reported so far, showing its promise as a new practical catalyst for APR of biomass-derived oxygenates to H 2. The excellent catalytic performance of the Pd/Fe 3O 4 catalyst was attributed to the enhanced synergistic effect between small Pd nanoparticles and magnetite in promoting the water–gas shift reaction, the rate-determining step in APR of EG over Pd-based catalysts.

Characterization and catalytic properties of Sn-modified rapidly quenched skeletal Ni catalysts in aqueous-phase reforming of ethylene glycol

Skeletal Ni (RQ Ni) catalyst was prepared by alkali leaching of rapidly quenched Ni 50Al 50 alloy. By impregnating RQ Ni with SnCl 4 followed by thermal treatment in inert atmosphere, homogeneous Sn-modified skeletal Ni (RQ Ni–Sn) catalysts were obtained. It was found that thermal treatment induces alloying of the deposited metallic Sn with Ni, forming Ni 3Sn alloy segregated on the catalyst surface. In aqueous-phase reforming of ethylene glycol, the RQ Ni catalyst was less selective in producing H 2 but more selective in producing alkanes than the Raney Ni catalyst described in the literature. This is attributed to the expansion of the lattice of RQ Ni favoring the dissociation of CO and, consequently, the methanation reaction consuming H 2. Moreover, the structural difference influences the reaction pathway, with the undesired C O cleavage pathway obstructed on RQ Ni. Modification of RQ Ni with Sn drastically improves the H 2 selectivity. On the RQ Ni 80Sn 20 catalyst, alkane production was virtually retarded, whereas H 2 selectivity as high as 98 mol% was achieved at high conversion. Based on the characterizations and previous findings, it is suggested that Sn may block the active sites for CO adsorption and/or dissociation, thus suppressing the undesired methanation reaction. On the other hand, bifunctional Ni–Sn ensembles may form, in which Sn facilitates H 2O dissociation while neighboring Ni adsorbs CO, thus promoting the desired water–gas shift reaction, leading to more H 2.