Steam Reforming Of Acetic Acid Research Articles

Modification of Nickel-Based Catalyst with Transition Metals to Tailor Reaction Intermediates and Property of Coke in Steam Reforming of Acetic Acid

Modification of Nickel-Based Catalyst with Transition Metals to Tailor Reaction Intermediates and Property of Coke in Steam Reforming of Acetic Acid

Hydrogen production from steam reforming of acetic acid over Pt–Ni bimetallic catalysts supported on ZrO2

Acetic acid, a model compound of bio-oil, was chosen to investigate the H2 production from steam reforming reaction using Pt and Ni catalysts supported on ZrO2. Ni crystallite sizes decreased with addition of Pt (from 23 to 15 nm), increasing the metallic dispersion (from 4.4 to 6.5%). A spillover effect was identified in bimetallic catalysts and caused a significant decrease of Ni reduction temperature. Although the Ni crystallite size in 15Ni/ZrO2 is larger, it showed 100% of conversion and the highest H2 yield (about 30%) during 30 h of reaction at 500 °C. In contrast to what was expect, the performance of bimetallic catalysts was not so good when compared to the monometallic Ni catalyst. 5Pt15Ni/ZrO2 and 1Pt15Ni/ZrO2 showed about 20% of H2 yield at the end of reaction. 1Pt/ZrO2 presented the worst catalytic performance; it produced more acetone, which can be correlated to its higher acidity, and deactivated very fast, with the highest coke formation rate. Coke was predominantly amorphous for all catalysts.

Highly active Nd-promoted Ni@Al2O3 core-shell catalyst for steam reforming of acetic acid: Insights of the remarkable coke resistance

Aiming at enhancing the coke resistance of Ni-based catalysts, the Nd-doped Ni@A2O3 core-shell catalysts were prepared and their catalytic performance was evaluated in the steam reforming of acetic acid (SRAA). The catalysts were characterized by BET, XRD, XRF, HRTEM, H2-TPR, NH3-TPD, and DTG. The catalytic performance was greatly enhanced by the incorporation of Nd, with decreased yields of CO, CH4, and acetone, increased yield of CO2, and remarkable carbon resistance. The decoking behavior of the spent catalyst was elucidated by H2O18-TSD. A low reaction temperature facilitates the formation of amorphous carbon, leading to catalyst deactivation. The decoking ability of the catalyst is greatly improved by the Nd incorporation but is also catalyzed by the exposed Ni surface. The Ni0.01Nd@Al catalyst greatly balanced the exposed Ni surface and the mobile lattice oxygen, showing the highest catalytic activity, lowest coke deposition, and superb decoking ability.

Coke-resistance enhancement of mesoporous γ-Al2O3 and MgO-supported Ni-based catalysts for sustainable hydrogen generation via steam reforming of acetic acid

Highly ordered mesoporous γ-Al2O3 particles and MgO materials were synthesized by evaporation induced self-assembly (EISA) and template-free hydrothermal co-precipitation routes, respectively. Ni, Ni–MgO, and Ni–La2O3-containing catalysts were prepared using a wet-impregnation method. The synthesized catalysts were characterized by N2 adsorption–desorption, XRD, SEM-EDS, DRIFTS, XPS, TGA-DTA, and Raman spectroscopy analysis. The mesoporous γ-Al2O3 catalyst support exhibited a high surface area of 245 m2/g and average pore volume of 0.481 cm3/g. The DRIFTS results indicate the existence of large Lewis's acid regions in the pure γ-Al2O3 and metal-containing catalysts. Catalytic activity tests of pure materials and metal-containing catalysts were carried out at the reaction temperature of 750 °C and a feed molar ratio of AA/H2O/Ar:1/2.5/2 over 3 h. Complete conversion of acetic acid and 81.75% hydrogen selectivity were obtained over the catalyst 5Ni@γ-Al2O3. The temperature and feed molar ratio had a noticeable impact on H2 selectivity and acetic acid conversion. Increasing the water proportion in the feed composition from 2.5 to 10 considerably improved the catalytic activity by increasing hydrogen selectivity from 81.75% to 91%. Although the Ni-based γ-Al2O3-supported catalysts exhibited higher activity performance compared to the Ni-based MgO-supported catalysts, they were not as resistant to coke formation as were MgO-supported catalysts. The introduction of MgO and La2O3 into the Ni@γ-Al2O3 and Ni@MgO catalysts' structures played a significant role in lowering the carbon formation (from 37.15% to 17.6%–12.44% and 12.17%, respectively) and improving the thermal stability of the catalysts by decreasing the agglomeration of acidic sites and reinforcing the adsorption of CO2 on the catalysts' surfaces. Therefore, coke deposition was reduced, and catalyst lifetime was improved.

Morphology dependent? Elucidating the catalyst structures of Ni/Ce0.75Zr0.25O2 in the steam reforming of acetic acid

In this work, the steam reforming of acetic acid was catalyzed by Ni-based catalysts supported on ceria-zirconia of different morphological structures (nanopolyhedra, nanorods, and nanocubes). The altered shapes led to the variation in catalyst properties, such as the exposed planes, ease of Ni reduction/oxidation, and carbon removal, which affected its catalytic performance. Additionally, it was found that the exposed planes present in cubic {100} and rod structures ({100} and {110}) enhanced the formation of Ni0 and subsequently promoted the reforming reaction. Moreover, oxygen vacancies and mobility properties of {100} and {110} exposed planes can promote the oxidation reaction of carbon, resulting in a stable catalyst for the reforming of acetic acid. The results also showed that the type of depositing carbons was influenced by the support morphology. All the catalysts showed a 100% acetic acid conversion with the 15Ni/NC-CeZr (cubic structure) catalyst exhibited the highest hydrogen yield.

Steam reforming of acetic acid for hydrogen production over Ni/CaxFeyO catalysts

Three Ni/CaxFeyO (x/y = 2:1, 1:1, 1:2) catalysts are prepared by impregnation method and applied in steam reforming of acetic acid as the model compound of bio-oil for hydrogen production. The effects of reaction temperature, steam to carbon ratio (S/C), liquid hourly space velocity (LHSV) on gas contents and H2 yield are carefully investigated and optimized. The fresh and used catalysts are characterized by BET, XRD, H2-TPR, CO2-TPD, SEM and TG methods. The experimental and characterization results show that the Ni/CaFe2O4 catalyst displays the best activity and stability among the three catalysts, providing 92.1% of H2 yield under S/C = 5, LHSV = 3.4 h−1 and at 600 °C. The strong interaction between Ni and CaFe2O4 support result in the formation of Ni–Fe alloy and Ca2Fe2O5, which shows the synergistic effects on the resistant to carbon deposition and metal sintering, thereby improving the activity and stability of the Ni/CaFe2O4 catalyst.

Optimization of the operating conditions for steam reforming of slow pyrolysis oil over an activated biochar-supported Ni–Co catalyst

Highly performing activated biochar-based catalysts were produced for steam reforming of slow pyrolysis oil. The raw biochar obtained from the slow pyrolysis step was physically activated with CO2 at 700 °C and 1.0 MPa and then employed as support. Preliminary tests on steam reforming of acetic acid at 600 °C showed that using activated biochar-supported catalysts containing 10 wt % Ni and 7 wt % Co led to a conversion above 90% with a relatively slow deactivation rate. When a representative organic model compounds mixture was used as feed, relatively fast deactivation of the catalyst was observed, probably due to the adsorption of heavy organic compounds, which could subsequently react to form not easily desorbable reaction intermediates. However, the dual Ni–Co catalysts exhibited a good performance during the steam reforming of a real slow pyrolysis oil at 750 °C, showing long stability and a constant carbon conversion of 65%.

Pore diameters of Ni/ZrO2 catalysts affect properties of the coke in steam reforming of acetic acid

Pore structures of support affect not only the dispersion of metals species, but also the catalytic stabilities and the properties of the generated coke in steam reforming reaction of acetic acid. This has been demonstrated in this study with Ni/ZrO2 catalysts of varied pore diameters. The results showed that the Ni/ZrO2 catalyst with the support calcined at 700 °C had the largest diameter, which facilitated the entering of nickel species into the pores, suppressing the migration and agglomerate in reduction of the catalysts. Although the catalysts with the varied pore diameters showed little impacts on the catalytic performances, the properties of the coke varied substantially. The catalyst with the large pore diameter favored the growth of the crystal carbon in the coke to a bigger size and was more tolerant to coke accumulation while maintained the catalytic stability. In addition, thermal stability, resistivity to oxidation, aromaticity, functionalities and the morphologies of the coke (i.e. carbon nanofibers, carbon nanotubes and bamboo-like structure) were all connected with the porous structures of the Ni/ZrO2 catalysts.

Producing Hydrogen from Steam Reforming of Bio-oil Derived Oxygenated Model Compounds by Utilizing Ce-Modified Ni/Attapulgite Catalysts

Steam reforming (SR) of bio-oil has been considered as one of the promising methods for hydrogen production. In this paper, cerium modified Ni/Attapulgite (ATP) catalysts were successfully synthesized by traditional chemical precipitation method and utilized for SR of various bio-oil derived oxygenated model compounds. The effect of Ce content on the structural properties of Ni/ATP was investigated by ICP-OES, N2 adsorption–desorption, XRD, H2-TPR and HRTEM characterizations. The results exhibited that 10Ce–Ni/ATP catalyst had the strongest metal-support interaction and highly dispersion of Ni species with smallest particle size of 6.21 nm. Therefore, it presented the maximum ethanol conversion of 97.21% and H2 yield of 83.15% at relative lower reaction temperature 500 °C during 4 h of SR of ethanol (SRE). In addition, it unfolded promising performance for SR of acetic acid (SRAA) and acetone (SRA). Furthermore, the influence of different oxygenates on the amount and nature of carbon deposits in used 10Ce–Ni/ATP catalyst was revealed by TG and Raman analyses. It found that the types of feedstock significantly affected the carbon species and amount and the formation of graphic layers around the Ni metal sites was the mainly factor for rapid deactivation of 10Ce–Ni/ATP during 4 h of SRA reaction.

Interaction of the reaction intermediates in co-reforming of acetic acid and ethanol impacts coke properties

Abstract Bio-oil is a mixture of organics and its steam reforming for production of hydrogen has attracted extensive attention. During steam reforming, the reaction intermediates derived from the varied organics in bio-oil might interact with each other, impacting composition/properties of the products. In this study, steam reforming of single or mixture of acetic acid and ethanol, the representatives of carboxylic acid and alcohol, were conducted with Ni/KIT-6 as the catalyst, aiming to probe the potential interaction of the reaction intermediates on the reforming reaction. The results showed that the interactions of the derivatives from acetic acid and ethanol did exist, enhancing conversion of reactants, formation of gaseous by-products and affecting coke properties. The co-reforming of ethanol and acetic acid generates more reaction intermediates bearing hydroxyl group that are difficult to be gasified and also forms more coke, leading to more significant catalyst deactivation. The coke formed from the co-reforming is not only prone to oxidation, but also showed distinct morphologies. Carbon nanotubes with coarse surface and hillocks was the main form of coke from steam reforming of ethanol or acetic acid, while coke from the co-reforming was mainly in the form of carbon nanofiber decorated with the hangnail-like substance or rope-like structures with no cavity and micrometers of length.

On the Support Effect and the Cr Promotion of Co Based Catalysts for the Acetic Acid Steam Reforming

This work focuses on the support effect of the performances of Co based catalysts for acetic acid steam reforming. SBA-15, a well ordered hexagonal mesoporous silica structure, and CeO2 have been selected as the supports, with the impact of chromium addition also being investigated. Better acetic acid steam reforming performances have been recorded for CeO2 compared to SBA-15 supported catalysts and, in particular, the 7Co/CeO2 catalyst showed the highest values of acetic acid conversions with enhanced H2 yields below 480 °C, in comparison to the other investigated catalytic formulations. In addition, more pronounced coke depositions and acetone concentrations have been obtained with CeO2 supported catalysts, due to the tendency of ceria to catalyse the ketonization reaction. Chromium addition to Co/SBA-15 catalysts led to an enhancement in the activity towards acetic acid steam reforming, while on CeO2 supported catalysts no improvement in the catalysts’ activity was observed. However, on both SBA-15 and CeO2 supported catalysts, Cr addition reduced the amount of coke deposited on the catalysts surface.

Impacts of residence time on transformation of reaction intermediates and coking behaviors of acetic acid during steam reforming

Liquid hourly space velocity (LHSV) is a critical factor in steam reforming as it not only determines process capacity of reformer, but also affect the properties of the coke formed via impacting the activation of the reactants and the formation of the products. In this study, the impacts of LHSV on the properties of the coke formed in steam reforming of acetic acid over Ni/SBA-15 catalyst were investigated. The results indicated that the increasing LHSV promoted the formation of the gaseous by-products and accelerated coking, as the low residence time was not conducive for activation of steam. The coke formed at the higher LHSV was more aromatic and have more fused but defective ring structures. Furthermore, at the low steam ratio in reactants, the high LHSV could also promoted the retainment of the carbonyl functionality in the coke. These phenomena are mainly due to the higher abundance of the organic species on surface of the catalyst under the high LHSV. In addition, not only the cavity of the carbon nanotube but also other morphologies the coke such as carbon nanofiber, bamboo-like structure and string beads-like structure was closely related to the LHSV, as LHSV impacted the reaction intermediates formed and further on the precursors of the coke.

Availability of steam impacts coke properties in steam reforming of acetic acid

Steam to carbon ratio (S/C) determines the availability of oxygen-containing species during steam reforming, which not only affect the amount of coke formed, but also might impact physicochemical properties of the coke generated. In this study, the effect of S/C on the coke formation in steam reforming of acetic acid was assessed. The results indicated that dissociative absorption of acetic acid generated the intermediates containing both CO and CC groups even at 100 °C. At low S/C, the insufficient ∗OH reacted with carbonaceous intermediates such as CHx to form more carbonyl species, leading to significant coking and lower gas yields. Sufficient ∗OH at high S/C facilitated transformation of the carbonyl-containing species into gases, minimizing coking. The varied amount of coke showed significant effect on the diffraction of metallic nickel phase, the particle size of Ni and the absorption for the Si–O–Si functional groups on spent catalysts. The coke formed at low S/C was more aromatic with high thermal stabilities, while the coke formed at high S/C was more aliphatic with low thermal stabilities. The involvement ∗OH species in coking process determined not only properties but also morphologies of the coke. The coke formed at low S/C showed bamboo-like, dendritic or twisted rope-like structure. While the higher S/C favored the generation of the carbon nanotubes with smooth outer surface.

Hydrogen production from acetic acid steam reforming over Ti-modified Ni/Attapulgite catalysts

Steam reforming of bio-oil derived oxygenates is a green and sustainable method for hydrogen production. In this work, hydrogen production from steam reforming of acetic acid (SRAA) was investigated over Ti-modified Ni/Attapulgite (ATP) catalysts that prepared via sequential precipitation technique. The effects of Ti additive, precipitation sequence and Ti-salt precursors (TiCl4, TiOSO4) on the structural and physicochemical properties of catalysts were characterized by N2 adsorption-desorption, XRD, FT-IR, HRTEM, XPS, H2-TPR and NH3-TPD. These results indicated that the interaction among Ti species, Ni active metal and ATP enhanced the reduction performance as well as weakened surface acidity of the Ni/ATP catalyst, and also promoted the electron transfer to form Niδ− species. Obviously, compared with Ti precursor salts, the precipitation sequences played a key role in determining the surface properties of Ti-modified catalysts. Among them, the Ni–TiS/ATP catalyst synthesized by co-precipitation method exhibited better reducibility and lower surface acidity, as well as produced more Niδ− species and Niδ−-Ov-Ti3+ interface sites. Then the synergistic effects among the above-mentioned characters made the Ni–TiS/ATP catalyst present highest carbon conversion (93.4%) and H2 yield (77.6%) during SRAA reactions. The analyses of XRD, HRTEM and TG were implemented on used catalysts and discovered Ni–TiS/ATP catalysts shown promising metal sintering and coke resistance, which mainly caused by the presence of flat Ni–Ti@ATP structures. The possible conversion mechanism of acetic acid in the flat Ni–Ti@ATP structure of co-precipitation Ti-modified catalyst was also elucidated.

Stability of electroless pore-plated Pd-membranes in acetic acid steam membrane-reformers for ultra-pure hydrogen production

Electroless Pore-Plated (ELP-PP) membranes were successfully incorporated for the first time into a membrane reactor to produce hydrogen by acetic acid steam reforming (AASR), exhibiting adequate resistance against harsh operating conditions. Membranes were prepared onto tubular PSS supports modified with Pd/CeO2 particles and scaled-up around four times in length with high reproducibility respect previous studies. H2 permeances from 4.49 to 5.67·10−4 mol m−2 s−1 Pa-0.5 were found for pure H2 at 350–450 °C, decreasing for mixtures due to concentration-polarization at higher pressures but also certain inhibition caused by CO2 at pressures below 50 Pa0.5. The combination of membranes with Ni/SBA-15 catalysts in packed-bed membrane reactors (PBMR) evidenced the simultaneous improvement of acetic acid conversion and hydrogen yield respect to analogous experiments in traditional packed-bed reactors (PBR). A very similar product distribution was obtained for both configurations, PBR and PBMR, when using fresh catalysts, although marked deviations were found in case of regenerating the catalysts. Then, higher selectivity towards coke reached for PBMR, which lead to around 30% for the most elevated pressure under investigation. However, even at these harsh conditions, the mechanical integrity of ELP-PP membranes was maintained. Thus, the benefits of combining catalysts and ELP-PP membranes in a PBMR for AASR were demonstrated.

Catalytic Behavior of Co-Based Catalysts in the Kinetic Study of Acetic Acid Steam Reforming

A kinetic model of acetic acid steam reforming is presented in this work on Co-based catalysts, accounting for the products distribution due to the main and side reactions. The Cr-promoted catalyst...

Effect of the incorporation of reducibility promoters (Cu, Ce, Ag) in Co/ CaSBA ‐15 catalysts for acetic acid steam reforming

In this work, we have faced the problem associated with the addition of Ca to Co/SBA-15, which gave rise to an increase in the dispersion of the particles at the expense of increasing its reduction temperature, thus limiting its reducibility as demonstrated by XPS. This detrimental effect has been solved by the inclusion of reducibility promoters such as Cu, Ag and Ce. All these promoters led to an increase in the acetic acid conversion attributed to their beneficial effect in the catalyst reducibility. With the inclusion of Ce to Co/CaSBA-15, the high dispersion was maintained while the percentage of reduced Co species increased by ~90% compared with Co/CaSBA-15, leading to the best catalytic performance (X ~ 99%, YH2 = 71.8%) after 5 hours TOS in the acetic acid steam reforming (S/C = 2) at 600°C using a WHSV = 30.1 hours−1. Furthermore, Co-Ce/CaSBA-15 showed good stability with hydrogen yield close to the thermodynamic value. These results highlight the necessity of combining both dispersing additives and promoters of reducibility to enhance the catalytic performance in steam reforming.

Hydrogen production from acetic acid steam reforming over nickel-based catalyst synthesized via MOF process

In our earlier work, we have reported that Ni supported on γ-Al2O3–La2O3–CeO2 (ALC) catalyst prepared via metal organic framework (MOF) was more active for acetic acid steam reforming (AASR) [1]. Here we report detailed study on the performance of this catalyst for AASR. Effects of operating conditions such as temperatures (400–650 °C), steam to carbon molar ratio (S/C) and feed flow rate (1.5–5.5 mL/h) were evaluated and optimized. Results showed an excellent activity for AASR at the molar ratio S/C = 6.5, feed flow rate = 2.5 mL/h and, at 600 °C with almost total conversion and more than 90% of H2 yield. The ordered porous structure of embedded nickel supported catalyst promotes excellent steam reforming activity and water gas shift reaction even at low temperatures, which leads to the good stable behaviour up to 36 h of TOS. The coke formation was also significantly suppressed by ALC support. Catalyst regenerated by passing oxygen at 500 °C and followed by reduction in hydrogen also show a good activity. Catalysts were characterized by DT-TGA, XRD, TEM, H2-TPR and N2-adsorption-desorption to understand the micro structure and coke deposition behaviour.

Ordinary clay as a support of nickel catalyst for steam reforming of acetic acid: Impacts of pretreatments of clay on catalytic behaviors

Ordinary clay as a support of nickel catalyst for steam reforming of acetic acid: Impacts of pretreatments of clay on catalytic behaviors

Steam reforming of acetic acid over Ni/biochar catalyst treated with HNO3: Impacts of the treatment on surface properties and catalytic behaviors

Biochar is a major product from the pyrolysis of biomass, which can be potentially used as the low costly support of nickel catalyst for steam reforming reactions. In this study, the rice husk-derived biochar supported nickel catalysts were prepared and the impacts of the treatment of the biochar support with HNO3 on catalytic performance of the Ni/biochar catalysts in steam reforming of acetic acid were investigated. The results showed that the treatment of the biochar with the varied concentration of HNO3 led to the change of the hydrophilicity, the pore structure, distribution of functionalities on surface of biochar, weakening of the interaction between nickel and biochar, increased size of metallic nickel, decreased lower nickel dispersion and enhanced abundance and strength of acidic sites. Among these aspects, the hydrophobicity showed the most significant effects on the catalytic activity for steam reforming of acetic acid. The Ni/biochar catalyst with medium hydrophobicity showed superior catalytic activity, as it showed capability for strong adsorption of the reaction intermediates with the C–O–C aliphatic structures and for gasification of the reaction intermediates with carbonyl functionalities. The Ni/biochar catalyst with too high hydrophobicity could not effectively gasifying the intermediates bearing CO and showed the low activity and high coking tendency.