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

Tailoring the Brønsted acidity of Ti-OH species by regulating Pt-TiO2 interaction

Bifunctional catalysts comprising metal and acid sites are commonly used for many reactions. Interfacial acid sites impact intermediate reactions more than other sites. However, controlling the type and amounts of interfacial acid sites by regulating metal-support interaction (MSI) via traditional methods is difficult. Thus, the influence of MSI on interfacial acid sites remains unclear. We prepared Pt-mTiO2/α-Al2O3 (m represents the cycle number of TiO2) catalysts via atomic layer deposition (ALD). New Brønsted acid sites were generated via Pt-TiO2 interaction, and the acidity was precisely regulated by regulating Pt-TiO2 interaction by changing the TiO2 nanolayer thickness. We chose levulinic acid (LA) hydrogenation as a model reaction. The catalytic activity varied with the TiO2 nanolayer thickness and was linearly correlated with the Ti-OH species (Brønsted acid) content. Pt-40TiO2/α-Al2O3, with the highest acid site content of 0.486 mmol/g, exhibited the best catalytic activity. Hydrogen spillover and water dissociation at the Pt-TiO2 interface promoted Ti-OH species generation.

Chitosan-Lignin Carbon Framework Encapsulated Cu Catalyst Facilitates Base-free Hydrogen Evolution from Methanol/Water

Methanol reforming in aqueous solution provides a significantly attractive and promising pathway to release hydrogen with mild H2 release condition and high H2 storage capacity. Exploring non-noble metal-based catalysts with...

Heterogeneous Catalysis in Water

Heterogeneous catalytic processes produce the majority of the fuels and chemicals in the chemical industry and have kept improving the welfare of human beings for centuries. Although most of the heterogeneous catalytic reactions occur at the gas-solid interface, numerous cases have demonstrated that the condensed water near the active site and/or the aqueous phase merging the catalysts play positive roles in enhancing the performance of heterogeneous catalysts and creating novel catalytic conversion routes. We enumerate the traditional heterogeneous catalytic reactions that enable significant rate/selectivity promotion in the aqueous phase or adsorbed micro water environment and discuss the role of water in specific systems. Some of the novel heterogeneous reactions achieved with only the assistance of the aqueous phase have been summarized. The development of reactions with the participation of the aqueous phase/water and the investigation of the role of water in the heterogeneous catalytic reactions will open new horizons for catalysts with better activity, improved selectivity, and novel processes.

Supported Pt-Cu bimetallic catalysts: preparation and synergic effects in their catalytic oxidative degradation of aniline

Catalytic Fenton oxidation is an effective way to remove organic pollutants in water, and the performance of the catalyst is a key issue for the competiveness of this method. In this work, various supported bimetallic Pt–Cu catalysts were prepared by different impregnation methods and their performances for catalytic Fenton oxidation of aniline in water were investigated. In the different impregnation methods employed, factors including the reduction method of the metal precursor, type of catalytic support, and loading of metal were investigated. The effect of different reduction methods on actual loadings of the active components on the supported Pt–Cu catalysts showed the order of (i) H₂ reduction > (ii) liquid phase methanal reduction. Meanwhile, compared with the monometallic catalysts, the Pt–Cu alloy phase (mainly in the form of PtCu₃) was generated and the specific surface area was significantly reduced for the bimetallic catalysts. In the process of Fenton catalytic oxidation of aniline, it was found that most of the prepared catalysts had a certain catalytic activity for H₂O₂ accompanied with aniline degradation. It was found that Pt_0.5Cu_1.5/AC (where AC denotes activated carbon) exhibited superb catalytic activity compared with all other prepared catalysts. In particular, aniline was almost completely mineralized in a neutral solution (500 mg L⁻¹ aniline, 0.098 mol L⁻¹ H₂O₂) after 60 min at 50 °C using Pt–Cu/AC (Pt: 0.5%, Cu: 1.5%). The characterization results showed that the Pt and Cu components were rather evenly distributed on the AC support for this catalyst. More importantly, there was an obvious synergic effect on the supported bimetallic catalyst between the Pt and Cu components for the catalytic oxidation of aniline.

An AC supported Pt–Cu catalyst prepared with a new methanal reduction method was found to be quite effective for catalytic Fenton oxidation of aniline in water. The Pt and Cu components showed a synergic effect for the catalytic process.

Continuous aqueous phase reforming of a synthetic brewery wastewater with Pt/C and PtRe/C catalysts for biohydrogen production

This work investigates H₂ production through aqueous phase reforming (APR) of synthetic brewery wastewater in a continuous fixed bed reactor with Pt and PtRe (3 wt %) catalysts supported on activated carbon. The influence of weight hourly space velocity (WHSV) and superficial Ar gas flow velocity (V_Ar) was assessed for the sake of optimisation, while reaction temperature and pressure were maintained at 225 °C and 28 bar, respectively. H₂ production was found to be higher using the PtRe catalyst at the lowest WHSV (0.03 h^-1) and highest V_Ar (0.8 cm s^-1). The comparison of the maximum H₂ production obtained in this work (27.9 μmol min^-1) with other treatment processes shows the potential of the application of APR process for H₂ production from brewery wastewater. Despite the different reaction conditions tested, the catalysts showed deactivation with time on stream, which was related to the formation of solid deposits on the surface of the catalysts. Therefore, future research should be related to the development of more stable catalysts, strategies that avoid deactivation by coking and regeneration processes.

Microemulsion Derived Titania Nanospheres: An Improved Pt Supported Catalyst for Glycerol Aqueous Phase Reforming

Glycerol aqueous phase reforming (APR) produces hydrogen and interesting compounds at relatively mild temperatures. Among APR catalysts investigated in literature, little attention has been given to Pt supported on TiO₂. Therefore, herein we propose an innovative titania support which can be obtained through an optimized microemulsion technique. This procedure provided high surface area titania nanospheres, with a peculiar high density of weak acidic sites. The material was tested in the catalytic glycerol APR after Pt deposition. A mechanism hypothesis was drawn, which evidenced the pathways giving the main products. When compared with a commercial TiO₂ support, the synthetized titania provided higher hydrogen selectivity and glycerol conversion thanks to improved catalytic activity and ability to prompt consecutive dehydrogenation reactions. This was correlated to an enhanced cooperation between Pt nanoparticles and the acid sites of the support.

Bimetallic Pt-Co Catalysts for the Liquid-Phase WGS

Bimetallic Pt-Co catalysts derived from cobalt aluminate spinel were investigated in the liquid-phase water–gas shift (WGS) reaction and CO hydrogenation. Liquid-phase WGS is a key reaction in the aqueous-phase reforming (APR) of polyols; thus, WGS activity is essential to formulate good APR catalysts. In this work, catalysts with different Pt/Co molar ratios were synthesized together with a reference Pt/alumina. All the synthesized catalysts were characterized by various techniques in order to gain knowledge on their structural and surface characteristics. WGS activity was tested with a feedstream of CO/H2O = 1/15 (space-time of 76.8 kgcat·s/molCO), isothermal operation at 260 °C and 50 bar, for 10 TOS. Bimetallic Pt-Co catalysts showed improved activity in liquid-phase WGS in comparison to bare Co or Pt catalysts, which was ascribed to the synergistic effect. Despite being subjected to an increased hydrogen concentration in the feedstream (H2/CO between 0 and 12/3), these catalysts maintained a preferential selectivity towards WGS activity. In addition, the effect of temperature (220–260 °C) and pressure (25–50 bar) was investigated over a catalyst with 0.3Pt/CoAl. CO conversion and CO2 yield were more sensitive to temperature, while a higher pressure favored methane production. The measured activation energy in the 220–260 °C temperature range was 51.5 kJ/mol.

Platinum Based Catalysts in the Water Gas Shift Reaction: Recent Advances

The water gas shift (WGS) is an equilibrium exothermic reaction, whose corresponding industrial process is normally carried out in two adiabatic stages, to overcome the thermodynamic and kinetic limitations. The high temperature stage makes use of iron/chromium-based catalysts, while the low temperature stage employs copper/zinc-based catalysts. Nevertheless, both these systems have several problems, mainly dealing with safety issues and process efficiency. Accordingly, in the last decade abundant researches have been focused on the study of alternative catalytic systems. The best performances have been obtained with noble metal-based catalysts, among which, platinum-based formulations showed a good compromise between performance and ease of preparation. These catalytic systems are extremely attractive, as they have numerous advantages, including the feasibility of intermediate temperature (250–400 °C) applications, the absence of pyrophoricity, and the high activity even at low loadings. The particle size plays a crucial role in determining their catalytic activity, enhancing the performance of the nanometric catalytic systems: the best activity and stability was reported for particle sizes < 1.7 nm. Moreover the optimal Pt loading seems to be located near 1 wt%, as well as the optimal Pt coverage was identified in 0.25 ML. Kinetics and mechanisms studies highlighted the low energy activation of Pt/Mo2C-based catalytic systems (Ea of 38 kJ·mol−1), the associative mechanism is the most encountered on the investigated studies. This review focuses on a selection of recent published articles, related to the preparation and use of unstructured platinum-based catalysts in water gas shift reaction, and is organized in five main sections: comparative studies, kinetics, reaction mechanisms, sour WGS and electrochemical promotion. Each section is divided in paragraphs, at the end of the section a summary and a summary table are provided.

Kinetic Modelling of the Aqueous-Phase Reforming of Fischer-Tropsch Water over Ceria-Zirconia Supported Nickel-Copper Catalyst

In the Fischer–Tropsch (FT) synthesis, a mixture of CO and H2 is converted into hydrocarbons and water with diluted organics. This water fraction with oxygenated hydrocarbons can be processed through aqueous-phase reforming (APR) to produce H2. Therefore, the APR of FT water may decrease the environmental impact of organic waters and improve the efficiency of the FT process. This work aimed at developing a kinetic model for the APR of FT water. APR experiments were conducted with real FT water in a continuous packed-bed reactor at different operating conditions of temperature (210–240 °C), pressure (3.2–4.5 MPa) and weight hourly space velocity (WHSV) (40–200 h−1) over a nickel-copper catalyst supported on ceria-zirconia. The kinetic model considered C1-C4 alcohols as reactants, H2, CO, CO2 and CH4 as the gaseous products, and acetic acid as the only liquid product. The kinetic model included seven reactions, the reaction rates of which were expressed with power law equations. The kinetic parameters were estimated with variances and confidence intervals that explain the accuracy of the model to estimate the outlet liquid composition resulting from the APR of FT water. The kinetic model developed in this work may facilitate the development of APR to be integrated in a FT synthesis process.

Hydrogen from Renewables: A Case Study of Glycerol Reforming

Biomass is an interesting candidate raw material for the production of renewable hydrogen. The conversion of biomass into hydrogen can be achieved by several processes. In particular, this short review focuses on the recent advances in glycerol reforming to hydrogen, highlighting the development of new and active catalysts, the optimization of reaction conditions, and the use of non-innocent supports as advanced materials for supported catalysts. Different processes for hydrogen production from glycerol, especially aqueous phase reforming (APR) and steam reforming (SR), are described in brief. Thermodynamic analyses, which enable comparison with experimental studies, are also considered. In addition, research advances in terms of life cycle perspective applied to support R&D activities in the synthesis of renewable H2 from biomass are presented. Lastly, also featured is an evaluation of the studies published, as evidence of the increased interest of both academic research and the industrial community in biomass conversion to energy sources.

Catalytic Transfer Hydrogenation of Biomass-Derived Substrates to Value-Added Chemicals on Dual-Function Catalysts: Opportunities and Challenges

Aqueous-phase hydrodeoxygenation (APH) of bioderived feedstocks into useful chemical building blocks is one the most important processes for biomass conversion. However, several technological challenges, such as elevated reaction temperature (220-280 °C), high H₂ pressure (4-10 MPa), uncontrollable side reactions, and intensive capital investment, have resulted in a bottleneck for the further development of existing APH processes. Catalytic transfer hydrogenation (CTH) under much milder conditions with non-fossil-based H₂ has attracted extensive interest as a result of several advantageous features, including high atom efficiency (≈100 %), low energy intensity, and green H₂ obtained from renewable sources. Typically, CTH can be categorized as internal H₂ transfer (sacrificing small amounts of feedstocks for H₂ generation) and external H₂ transfer from H₂ donors (e.g., alcohols, formic acid). Although the last decade has witnessed a few successful applications of conventional APH technologies, CTH is still relatively new for biomass conversion. Very limited attempts have been made in both academia and industry. Understanding the fundamentals for precise control of catalyst structures is key for tunable dual functionality to combine simultaneous H₂ generation and hydrogenation. Therefore, this Review focuses on the rational design of dual-functionalized catalysts for synchronous H₂ generation and hydrogenation of bio-feedstocks into value-added chemicals through CTH technologies. Most recent studies, published from 2015 to 2018, on the transformation of selected model compounds, including glycerol, xylitol, sorbitol, levulinic acid, hydroxymethylfurfural, furfural, cresol, phenol, and guaiacol, are critically reviewed herein. The relationship between the nanostructures of heterogeneous catalysts and the catalytic activity and selectivity for C-O, C-H, C-C, and O-H bond cleavage are discussed to provide insights into future designs for the atom-economical conversion of biomass into fuels and chemicals.

Sibunit-Supported Mono- and Bimetallic Catalysts Used in Aqueous-Phase Reforming of Xylitol

Carbon-supported mono- and bimetallic catalysts prepared via incipient wetness impregnation were systematically studied in aqueous-phase reforming (APR) of xylitol aiming at hydrogen production from biomass. The catalytic performance of several VIII group metals and their combinations, such as Pt, Ni, Pt–Ni, Re, Pt–Re, Ru, Pt–Ru, and Pt–Co, was compared for xylitol APR in a fixed-bed reactor at 225 °C and 29.7 bar (N₂). Ni/C, Ru/C, and Re/C catalysts displayed significantly lower activity compared to others. Activity and selectivity to H₂ of bimetallic Pt–Ni/C, Pt–Co/C, and Pt–Ru/C catalysts were close to that of Pt/C. Pt–Re/C catalyst showed an outstanding performance which was accompanied by a shift of the reaction pathways to the alkane formation and thereby lower hydrogen selectivity. Addition of the second metal to Pt was not found to be beneficial for hydrogen production, thus leaving Pt/C as the optimum carbon-supported catalyst.

Butanol reforming: an overview on recent developments and future aspects

Recently, hydrogen is utilized by numerous chemical industries as an alternate over non-renewable fuels, and surely it will be considered as an important fuel in the near future. This paper reports a review of various reforming technologies for hydrogen production from butanol produced by fermentation of feedstocks like wheat, sugar beets, sugar cane, etc. with a number of aspects involving selection of an appropriate catalyst to suppress undesirable products as many reforming reactions are dependent on the catalyst properties to enhance the formation of significant fuels which may fulfill the future energy needs. An overview of butanol reforming processes with experimental and theoretical studies in order to grasp possibilities and restrictions of these processes is not comprehensively presented yet. In this paper, an assessment of published articles in brief related to essential parameters to carry out a pertinent research in the future is presented for the advancement of fuel processing technologies.

Catalytic Reforming of Oxygenates: State of the Art and Future Prospects

This Review describes recent advances in the design, synthesis, reactivity, selectivity, structural, and electronic properties of the catalysts for reforming of a variety of oxygenates (e.g., from simple monoalcohols to higher polyols, then to sugars, phenols, and finally complicated mixtures like bio-oil). A comprehensive exploration of the structure-activity relationship in catalytic reforming of oxygenates is carried out, assisted by state-of-the-art characterization techniques and computational tools. Critical emphasis has been given on the mechanisms of these heterogeneous-catalyzed reactions and especially on the nature of the active catalytic sites and reaction pathways. Similarities and differences (reaction mechanisms, design and synthesis of catalysts, as well as catalytic systems) in the reforming process of these oxygenates will also be discussed. A critical overview is then provided regarding the challenges and opportunities for research in this area with a focus on the roles that systems of heterogeneous catalysis, reaction engineering, and materials science can play in the near future. This Review aims to present insights into the intrinsic mechanism involved in catalytic reforming and provides guidance to the development of novel catalysts and processes for the efficient utilization of oxygenates for energy and environmental purposes.

Improved synthesis and hydrothermal stability of Pt/C catalysts based on size-controlled nanoparticles

A novel method for the preparation of stable Pt/C catalysts with size-controlled nanoparticles has been developed.

Aqueous-phase reforming of crude glycerol: effect of impurities on hydrogen production

Fatty acid salt contaminants proved detrimental for efficient hydrogen production in the aqueous phase reforming of an industrial crude glycerol.

Aqueous phase reforming and hydrodeoxygenation of ethylene glycol on Pt/SiO2–Al2O3: effects of surface acidity on product distribution

Aqueous-phase reforming and hydrodeoxygenation of ethylene glycol were investigated on Pt/SiO₂–Al₂O₃. The Pt/SiO₂–Al₂O₃ with Si/Al ratio of 0.1 showed a higher activity due to an abundant acidic sites with small platinum crystallites and a lower coke deposition.

Heterogeneous and homogeneous catalysis for the hydrogenation of carboxylic acid derivatives: history, advances and future directions

Recent progress in hydrogenation of carboxylic acid derivatives is described with a particular focus on the catalyst performance, composition and reaction mechanism.

Aqueous phase reforming of ethylene glycol on Pt/CeO2–ZrO2: effects of cerium to zirconium molar ratio

The superior activity of aqueous-phase reforming of ethylene glycol on optimal Pt/CeO₂–ZrO₂ was attributed to the strongly interacting platinum species on the oxygen vacancy defect sites of the support, forming thermally-stable platinum crystallites.