High Coke-Resistance Pt/Mg1-xNixO Catalyst for Dry Reforming of Methane

A Review of the Design and Performance of Catalysts for Hydrothermal Gasification of Biomass to Produce Hydrogen-Rich Gas Fuel

Supercritical water gasification has emerged as a promising technology to sustainably convert waste residues into clean gaseous fuels rich in combustible gases such as hydrogen and methane. The composition and yield of gases from hydrothermal gasification depend on process conditions such as temperature, pressure, reaction time, feedstock concentration, and reactor geometry. However, catalysts also play a vital role in enhancing the gasification reactions and selectively altering the composition of gas products. Catalysts can also enhance hydrothermal reforming and cracking of biomass to achieve desired gas yields at moderate temperatures, thereby reducing the energy input of the hydrothermal gasification process. However, due to the complex hydrodynamics of supercritical water, the literature is limited regarding the synthesis, application, and performance of catalysts used in hydrothermal gasification. Hence, this review provides a detailed discussion of different heterogeneous catalysts (e.g., metal oxides and transition metals), homogeneous catalysts (e.g., hydroxides and carbonates), and novel carbonaceous catalysts deployed in hydrothermal gasification. The article also summarizes the advantages, disadvantages, and performance of these catalysts in accelerating specific reactions during hydrothermal gasification of biomass, such as water-gas shift, methanation, hydrogenation, reforming, hydrolysis, cracking, bond cleavage, and depolymerization. Different reaction mechanisms involving a variety of catalysts during the hydrothermal gasification of biomass are outlined. The article also highlights recent advancements with recommendations for catalytic supercritical water gasification of biomass and its model compounds, and it evaluates process viability and feasibility for commercialization.

Dry Reforming of Methane with Ni Supported on Mechanically Mixed Yttria-Zirconia Support

This study focuses on CH4 reforming with CO2 over Ni supported on yttria mixed with zirconia support. Different loading of yttria was used to enhance the performance of Ni towards achieving the optimum activity. The physicochemical properties of both fresh calcined and used catalysts were studied using a range of characterization techniques. The specific surface area measurement by the BET method showed a progressive increase in the area with an increase in yttria loading. The monoclinic (m- ZrO2) and tetragonal (t- ZrO2) phases were identified on all the samples by the XRD analysis. A reduction in the intensity of m- ZrO2 was observed on adding Ni to the catalysts while the diffraction pattern of crystalline yttria was not identified. The reducibility analysis showed the influence of yttria. It induces the formation of NiYO3 species with stronger active metal-support interaction. From the catalytic test, 5Ni/10Y-Z-3215 had the highest feed conversion of about 68 and 88% for CH4 and CO2 respectively. The TEM analysis showed a uniform dispersion of NiO particles over the mixed yttria-zirconia support with no agglomeration of the active metal particles after the reaction. The measurement of the quantity of carbon deposits by the TGA revealed that the increase in yttria loading enhanced the gasification of carbon deposits with 5Ni/20Y-Z-3215 recording the lowest weight loss of about 28%.

Graphical Abstract

High Active Co/Mg1-xCex3+O Catalyst: Effects of Metal-Support Promoter Interactions on CO2 Reforming of CH4 Reaction

Co/Mg1−XCe3+XO (x = 0, 0.03, 0.07, 0.15; 1 wt% cobalt each) catalysts for the dry reforming of methane (DRM) reaction were prepared using the co-precipitation method with K2CO3 as precipitant. Characterization of the catalysts was achieved by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). The role of several reactant and catalyst concentrations, and reaction temperatures (700–900 °C) on the catalytic performance of the DRM reaction was measured in a tubular fixed-bed reactor under atmospheric pressure at various CH4/CO2 concentration ratios (1:1 to 2:1). Using X-ray diffraction, a surface area of 19.2 m2.g−1 was exhibited by the Co/Mg0.85Ce3+0.15O catalyst and MgO phase (average crystallite size of 61.4 nm) was detected on the surface of the catalyst. H2 temperature programmed reaction revealed a reduction of CoO particles to metallic Co0 phase. The catalytic stability of the Co/Mg0.85Ce3+0.15O catalyst was achieved for 200 h on-stream at 900 °C for the 1:1 CH4:CO2 ratio with an H2/CO ratio of 1.0 and a CH4, CO2 conversions of 75% and 86%, respectively. In the present study, the conversion of CH4 was improved (75%–84%) when conducting the experiment at a lower flow of oxygen (1.25%). Finally, the deposition of carbon on the spent catalysts was analyzed using TEM and Temperature programmed oxidation-mass spectroscopy (TPO-MS) following 200 h under an oxygen stream. Better anti-coking activity of the reduced catalyst was observed by both, TEM, and TPO-MS analysis. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA   License (https://creativecommons.org/licenses/by-sa/4.0). 

Enhancement of CO2 Reforming of CH4 Reaction Using Ni,Pd,Pt/Mg1−xCex4+O and Ni/Mg1−xCex4+O Catalysts

Catalysts Ni/Mg1−xCex4+O and Ni,Pd,Pt/Mg1−xCex4+O were developed using the co-precipitation–impregnation methods. Catalyst characterization took place using XRD, H2-TPR, XRF, XPS, Brunauer–Emmett–Teller (BET), TGA TEM, and FE-SEM. Testing the catalysts for the dry reforming of CH4 took place at temperatures of 700–900 °C. Findings from this study revealed a higher CH4 and CO2 conversion using the tri-metallic Ni,Pd,Pt/Mg1−xCex4+O catalyst in comparison with Ni monometallic systems in the whole temperature ranges. The catalyst Ni,Pd,Pt/Mg0.85Ce4+0.15O also reported an elevated activity level (CH4; 78%, and CO2; 90%) and an outstanding stability. Carbon deposition on spent catalysts was analyzed using TEM and Temperature programmed oxidation-mass spectroscopy (TPO-MS) following 200 h under an oxygen stream. The TEM and TPO-MS analysis results indicated a better anti-coking activity of the reduced catalyst along with a minimal concentration of platinum and palladium metals.

Effect of La2O3 as a Promoter on the Pt,Pd,Ni/MgO Catalyst in Dry Reforming of Methane Reaction

Pt,Pd,Ni/MgO, Pt,Pd,Ni/Mg0.97La3+0.03O, Pt,Pd,Ni/Mg0.93La3+0.07O, and Pt,Pd,Ni/Mg0.85La3+0.15O (1% of each of the Ni, Pd, and Pt) catalysts were prepared by a surfactant-assisted co-precipitation method. Samples were characterized by the XRD, XPS, XRF, FT-IR, H2-TPR, TEM, the Brunauer–Emmett–Teller (BET) method, and TGA and were tested for the dry reforming of methane (DRM). TEM and thermal gravimetric analysis (TGA) methods were used to analyze the carbon deposition on spent catalysts after 200 h at 900 °C. At a temperature of 900 °C and a 1:1 CH4:CO2 ratio, the tri-metallic Pt,Pd,Ni/Mg0.85La3+0.15O catalyst with a lanthanum promoter showed a higher conversion of CH4 (85.01%) and CO2 (98.97%) compared to the Ni,Pd,Pt/MgO catalysts in the whole temperature range. The selectivity of H2/CO decreased in the following order: Pt,Pd,Ni/Mg0.85La3+0.15O > Pt,Pd,Ni/Mg0.93La3+0.07O > Pt,Pd,Ni/Mg0.97La3+0.03O > Ni,Pd,Pt/MgO. The results indicated that among the catalysts, the Pt,Pd,Ni/Mg0.85La23+0.15O catalyst exhibited the highest activity, making it the most suitable for the dry reforming of methane reaction.