Shaping of Porous CeO2 Powders into Highly Active Catalyst Carriers

CeO₂ is attracting more and more attention because of its outstanding performance in heterogeneous catalysis, as an active support and a reaction promoter in reactions of industrial interest. We herein describe a novel and scalable manufacturing process of mm-sized CeO₂ spheres by a combination of extrusion and spheronization of CeO₂ porous powders. In this study, wet paste formulation and fabrication procedures were optimized, and as a result methylcellulose was identified as the best plasticizer for paste extrusion to provide well-defined spherical shapes and smooth surfaces, as well as reproducible batches. After nickel impregnation (10 wt %), the catalytic performance of CeO₂ supports was evaluated in the CO₂ methanation reaction (T = 250-350 °C, P = 5 bar·g) and compared with that of commercial Al₂O₃ spheres doped or not with CeO₂. These novel CeO₂-based catalysts are easily reduced at a moderate temperature and more active than the Al₂O₃ analogues, particularly at low reaction temperatures and small reactor volumes, properties that make their implementation in emerging reactor configurations very promising.

Product regulation and catalyst deactivation during ex-situ catalytic fast pyrolysis of biomass over Nickel-Molybdenum bimetallic modified micro-mesoporous zeolites and clays

Ni-Mo bimetallic modified micro-mesoporous zeolite catalysts were prepared and employed in the process of ex-situ catalytic fast pyrolysis (CFP) of poplar to produce liquid fuel. Clay catalysts were incorporated to further improve the products quality. The mass yield of monocyclic aromatic hydrocarbons (MAHs) increased under the catalysis of composite catalysts AZM and NiMo/AZM. HAP&Zeolite dual catalyst system reduced coke yield of NiMo/AZM to 5.01 wt%. Through real-time monitoring of gas products, the catalytic performance of zeolites began to decrease after the ratio of biomass and catalyst was more than 1. A series of characterization results futher demonstrated that AZM and NiMo/AZM possessed more stable catalytic ability and higher catalytic activity during the whole CFP process. N2 adsorption-desorption measurement and Raman characterization illustrated the formation and structure of coke, catalyst deactivation and the protective mechanism of mesopores on micropores.

Na2WO4/Mn/SiO2 Catalyst Pellets for Upgrading H2S-Containing Biogas via the Oxidative Coupling of Methane

Biogas is a promising renewable energy source; however, it needs to be upgraded to increase its low calorific value. In this study, oxidative coupling of methane (OCM) was selected to convert it to a higher fuel standard. Prior to establishing the scaled-up OCM process, the effect of organic/inorganic binders on catalytic activity was examined. The selection of the binders and composition of the catalyst pellet influenced the pore structure, fracture strength, and catalytic activity of the catalyst pellets. It was also observed that the O2 supply from the inorganic binder is a key factor in determining catalytic activity, based on which the composition of the catalyst pellets was optimized. The higher heating value increased from 39.9 (CH4, Wobbe index = 53.5 MJ/Nm3) to 41.0 MJ/Nm3 (OCM product mixture, Wobbe index = 54.2 MJ/Nm3), achieving the fuel standard prescribed in many countries (Wobbe index = 45.5–55.0 MJ/Nm3). The reaction parameters (temperature, gas hourly space velocity, size of the reaction system, and the CH4/O2 ratio) were also optimized, followed by a sensitivity analysis. Furthermore, the catalyst was stable for a long-term (100 h) operation under the optimized conditions.

Recent advances in hydrogenation of CO2 into hydrocarbons via methanol intermediate over heterogeneous catalysts

This review provides recent advances in the conversion of CO₂ to methanol, methanol to hydrocarbons, and direct conversion of CO₂ to hydrocarbons via methanol intermediate over various monofunctional and bifunctional solid catalysts.

Extrusion and Characterization of High Si/Al Ratio ZSM-5 Using Silica Binder

Biogas upgrading is a key operation for transforming raw biogas into valuable biomethane that can be used as fuel or transported through pipelines. Pressure swing adsorption (PSA) is one possible technique that can be used for upgrading. ZSM-5 with high silica/aluminum (Si/Al) ratio has a reasonable CO2/CH4 selectivity and an almost linear CO2 adsorption isotherm, which can reduce power consumption. Extrusion of zeolites uses Al-based binders which can result in a denaturation and in a decrease of Si/Al ratio, promoting a steeper CO2 isotherm and also impacting the water adsorption. In this work, we have extruded a ZSM-5 (with a Si/Al = 200) using only silica-based binder. Different samples were obtained using different extrusion paste compositions and operating conditions and their textural properties characterized. The mechanical strength of the samples as well as the CO2, CH4, and H2O adsorption equilibrium isotherms at 303–343 K were measured. Our results show that it is possible to produce extrudates with mechanical resistance comparable to (or higher than) commercial zeolite materials with surface area reductions lower than 10% and little or no impact on the CO2/CH4 selectivity.

Effect of catalyst morphology and hydrogen co-feeding on the acid-catalysed transformation of acetone into mesitylene

Surface chemistry and pore topology affect mesitylene selectivity in acid-catalysed acetone condensation. Hydrogen improves both catalyst stability and condensation selectivity.

A Facile Strategy to Prepare Shaped ZSM-5 Catalysts with Enhanced Para-Xylene Selectivity and Stability for Toluene Methylation: The Effect of In Situ Modification by Attapulgite

A general strategy for preparing shaped toluene methylation catalysts with enhanced para-selectivity and stability is developed by extruding ZSM-5 zeolite with attapulgite as a binder. The novel attapulgite/ZSM-5 extrudate exhibited significantly higher para-selectivity and stability in comparison to the conventional alumina-bound ZSM-5 extrudate. The catalyst samples have been characterized by in situ X-ray diffraction, scanning electron microscope (SEM), NH₃ temperature programmed desorption (TPD), thermogravimetric analysis (TGA) as well as n-hexane/cyclohexane physical adsorption. The enhanced catalytic performance of attapulgite/ZSM-5 extrudate is correlated with the in-situ modification of acid sites in the catalyst by mobile alkaline species, which is introduced via extrusion with attapulgite. Moreover, a higher para-selectivity was obtained over attapulgite-bound modified ZSM-5 extrudate. Such facile and universal strategy of extruding ZSM-5 catalysts with attapulgite as binder could pave a way for preparation of shaped zeolite-base catalyst with enhanced catalytic performance.

Porosity Design of Shaped Zeolites for Improved Catalyst Lifetime in the Methanol-to-Hydrocarbons Reaction

Additional porosity, such as meso- and macropores, was introduced in zeolite extrudates with the intention intuit of improving the effective diffusivity of the catalysts. The samples were characterized in depth by nitrogen adsorption-desorption, mercury intrusion porosimetry, ammonia temperature programmed desorption and adsorption of pyridine followed by infrared spectroscopy. The results revealed no significant change in the acidity but an increase of the pore volume. According to significant improvement in the effective diffusivity, the samples were tested in the methanol-to-hydrocarbons reaction. The catalytic stability was greatly enhanced with an increase in the pore volume, demonstrating a relation between effective diffusivity and resistance to deactivation by coke formation. Further experiments also revealed a higher toluene adsorption capacity and a raise in the breakthrough time over the most porous samples due to better accessibility of toluene molecules into the active sites of the zeolite.

Scaling-Up of Bio-Oil Upgrading during Biomass Pyrolysis over ZrO2 /ZSM-5-Attapulgite

Ex situ catalytic biomass pyrolysis was investigated at both laboratory and bench scale by using a zeolite ZSM-5-based catalyst for selectively upgrading the bio-oil vapors. The catalyst consisted of nanocrystalline ZSM-5, modified by incorporation of ZrO₂ and agglomerated with attapulgite (ZrO₂ /n-ZSM-5-ATP). Characterization of this material by means of different techniques, including CO₂ and NH₃ temperature-programmed desorption (TPD), NMR spectroscopy, UV/Vis microspectroscopy, and fluorescence microscopy, showed that it possessed the right combination of accessibility and acid-base properties for promoting the conversion of the bulky molecules formed by lignocellulose pyrolysis and their subsequent deoxygenation to upgraded liquid organic fractions (bio-oil). The results obtained at the laboratory scale by varying the catalyst-to-biomass ratio (C/B) indicated that the ZrO₂ /n-ZSM-5-ATP catalyst was more efficient for bio-oil deoxygenation than the parent zeolite n-ZSM-5, producing upgraded bio-oils with better combinations of mass and energy yields with respect to the oxygen content. The excellent performance of the ZrO₂ /n-ZSM-5-ATP system was confirmed by working with a continuous bench-scale plant. The scale-up of the process, even with different raw biomasses as the feedstock, reaction conditions, and operation modes, was in line with the laboratory-scale results, leading to deoxygenation degrees of approximately 60 % with energy yields of approximately 70 % with respect to those of the thermal bio-oil.