1- Introduction

2- Materials & methods

3- Results & discussion

4- Process analysis

5- Conclusions

References

Abstract

The present paper describes the experimental tests for the recycling of fluid catalytic cracking catalysts (FCCCs). The process aims at the recovery of cerium (Ce) and lanthanum (La) as well as the reuse of the leaching solid residue that represents the actual problem in terms of global amount landfilled every year. Landfilling is still the main choice for the handling of such catalysts. This novel process proposes an alternative recycling approach that leads to the production of synthetic zeolites, that have several industrial applications. FCCC was leached by 1.5 mol/L of HNO3, HCl and H2SO4 solutions at 80 °C, for 2 h with a solid to liquid ratio of 20 %wt, and the two rare earth elements were recovered by precipitation with an overall yield in the range 70–80%. The solid residues from the leaching stage were used as the base material for the synthesis of the zeolites by means of a combined thermal-hydrothermal treatment. The characterization of the zeolites demonstrated that the Na-A phase was predominant over the Na-X phase. The zeolites were tested as sorbent material for CO2 separation from CH4, in order to simulate the upgrading of biogas to biomethane. The maximum adsorption rate of CO2 was 0.778 mol CO2/kg of zeolite at 3 bar, with a resulting CH4 recovery of 62% and 97 %vol as purity. Since the results in adsorption of CO2 were not satisfying, the same zeolites were used to remove heavy metals from a synthetic wastewater solution containing three metals. Equilibrium and kinetic models were also developed in order to describe the adsorption process. The maximum adsorption load was calculated by the Langmuir isotherm and resulted to be 24–32 mg/g for Ni, 52–60 mg/g for Zn and 122–181 mg/g for Cu. The results also showed that the kinetics of the adsorption process is almost fast, as after 1 h at least 95% of zinc and copper were removed, whereas the kinetics of nickel was slower for all the three zeolites. As a conclusion, the zeolites are more efficient in metal adsorption than CO2 capture, but other applications will be tested in the future.

Introduction

In the last fifty years, the significant expansion of the industrial, commercial and agricultural sectors was accompanied by a huge increase in production of petrochemical products and intermediates, as well as refined fuels like gasoline, diesel fuel, kerosene, jet fuel, naphtha, and gas oil. Hence, this led to massive use of catalysts for typical refinery processes like hydrotreating (HT), fluid catalytic cracking (FCC), catalytic reforming (CR), hydrodesulphurization (HDS), alkylation, isomerization. Many of them, once exhaust, can be regenerated by thermal treatments in presence of nitrogen, air or oxygen at a controlled temperature, but after a certain number of regenerations, the catalytic activity is irretrievably compromised. Other kinds of catalysts, like those for FCC, are poisoned by heavy metals such as nickel and vanadium, so that they cannot be regenerated and have to be replaced from time to time with fresh catalyst. The use of rare earths in FCC catalysts was driven by the need for more active and hydrothermally stable products with better yield performance. Rare earth oxides (REO) achieved these goals by enhancing catalytic activity and preventing the loss of acid sites during operation. REO concentration gradually increased over the years, and the average is currently in the range 3e5 %wt. China produces 95% of the world’s rare earths elements (REEs) supply, thus the recovery of such elements from industrial waste will play a crucial role in the future economy of the European countries (BASF, 2018).

1- Introduction

2- Experimental

3- Result and discussion

4- Conclusion

References

Abstract

Neodymium Vanadate (NdVO4) nanostructures were successfully synthesized via a modified solid state method in the presence of ligand. These nanoparticles were further used as a photocatalyst. Primarily the best structural formations and smallest crystallite sizes of the systems were identified and optimized by changing the calcination time, calcination temperature and molar ratio of the ligand. The cationic (Methyl Violet (MV)), and anionic (Eosin Y (EY) and Eriochrome Black T (EBT)) dyes were used as a model to evaluate the photoactivity under UV–Vis irradiation. Several operational factors were examined to improve the photocatalytic efficiency include type of dye, type of light source, pH and dye concentration. As a result, the best efficiency in 5 ppm Eriochorome Black T at pH = 11 was achieved in the presence of 0.05 g NdVO4 nanocatalysts.

Introduction

The organic dyes (cationic and anionic dyes) are one of the most important environmental pollutants that are used in various industries such as textile, paper printing and pulp, rubber, plastics, leather, cosmetics, etc (Şahin et al., 2013; Elijah and Nwabanne, 2014). Aquatic environmental deterioration is a serious issue due to rapid urbanization and economic development; hence, the reductions of the hazardous contaminants from waste water are urgently required. Electroactive nanocatalysts are recently achieved a great attention in order to remove colorants from aquatic environments. Mx – orthovanadates (M: Na, Ca, Ba, Sc, Er, Nd …) are the inorganic compounds which consider for this application (Mahapatra et al., 2007). Among these compounds, neodymium vanadate is an important category of rare earth (RE) orthovanadates that has been synthesized by various techniques such as hydrothermal (Wu et al., 2005), solid-state reaction (Errandonea et al., 2014), sonochemical (Monsef et al., 2018), precipitation (Vosoughifar, 2016), sol-gel (Au et al., 1996) and microwave (Mahapatra et al., 2008a). NdVO4 powders are renowned as promising materials in photocatalytic, electrical, catalytic, laser, photoluminescence, optic, phosphors, polarizer properties (Mahapatra et al., 2008b; Yuvaraj et al., 2014; Selvan et al., 2009; Yao et al., 2010; Verma et al., 2016; Deng et al., 2008; Nguyen et al., 1997). Rare earth orthovanadates, especially in nanosized state, are highly promising for biomedical applications due to their high stability and nontoxicity (Lyadov and Kurilkin, 2016).

A thin disc-shaped Fenton-like catalyst sized 28.59*1.39 mm in diameter and thickness was produced by ball milling a hemi-dried silica xerogel with iron (III) acetylacetonate, followed by mold pressing and calcination. The developed compact catalyst facilitated its application and recovery. The whole fabrication process was free of wastewater emission. Plasticizers or binders indispensable for shaping commercial powders into compact green bodies were not necessary in the present method. The bulky catalyst was mesoporous and had a large surface area of 580 m2 /g, providing access to the activation of H2O2 by the active iron sites inside the sample. It removed 100% of methylene blue (MB) in solution with a total TOC reduction by 92.13% mainly via the Fenton degradation. No washing, chemical elution of the adsorbed dye before the next application was applied. After five cycles, ca.93% of the removal efficiency was maintained. The TOC reduction increased from the 1st to 3rd cycle and ca.88% of the initial capacity was kept after the 5th cycle, while the iron leaching was only 0.021% of the applied catalyst. The excellent performance of the bulky catalyst was due to its large surface area, uniformly distributed and chemically bonded iron species. The present work provides a scalable and green way to produce Fenton-like catalysts for environmental application.

Introduction

Dyes are used in industries including textile, leather manufacturing and printing, etc., leading to the formation of wastewaters containing dye molecules. Most synthetic dyes are difficult to degrade and have detrimental environment effects (Holkar et al., 2016). Using Fenton (-like) catalysts is an effective way to remove the dyes from wastewaters via degradation. It mainly utilizes iron-containing catalysts reacting with H2O2 to form free radicals as oxidants for the degradation of organic pollutants to carbon dioxide and water or to small molecules (Zhang et al., 2016; Li et al., 2019). Many different types of Fenton-like catalysts have been developed and applied in wastewater treatment (Nidheesh, 2015). Ironcontaining silica-based porous composites are among the developed Fenton-like catalysts which exhibited good dye removal performance. They were mostly prepared via hydrothermal reaction (Meng et al., 2016), sol-gel method (Chae et al., 2016) or impregnation (Ursachi et al., 2012; Rostamizadeh et al., 2018). These methods face a great challenge due to the emission of wastewater during the production of catalysts. Some of the Fenton-like catalysts have been proved efficient in removing methylene blue (MB), a commonly used dye in industries, from wastewaters (Zhang et al., 2016; Chai et al., 2016; Li et al., 2017; Mohamed et al., 2017; Li et al., 2018; Li et al., 2018; Li et al., 2018; He et al., 2018; Hu et al., 2019). However, with few exceptions (Li et al., 2018; Shi et al., 2019), most of such catalysts so far are in powder form, which makes their dispersion in wastewater and the recovery after the application a difficult work. In addition, the collection of used catalysts via filtration or centrifugation which are normally used in labs is actually not applicable at industrial scale, because of the small dosage of powders added in wastewaters.

1- Introduction

2- Computational methods

3- Results and discussion

4- Conclusions

References

ABSTRACT

The hydrogenation of nitrobenzene into aniline is one of industrially important reactions, but still remains great challenge due to the lack of highly active, chemo-selective and eco-friendly catalyst. By using extensive density functional theory (DFT) calculations, herein we predict that single Pt atom decorated g-C3N4 (Pt@g-C3N4) exhibits excellent catalytic activity and selectivity for the conversion of nitrobenzene into aniline under visible light. The overall activation energy barrier for the hydrogenation of nitrobenzene on single atom Pt@g-C3N4 catalyst is even lower than that of the bare Pt(111) surface. The dissociation of N–O bonds on single Pt atom is triggered by single hydrogen atom rather than double hydrogen atoms on the Pt(111) surface. Moreover, the Pt@g-C3N4 catalyst exhibits outstanding chemoselectivity towards the common reducible substituents, such as phenyl, –C=C, –C≡C and –CHO groups during the hydrogenation. In addition, the doped single Pt atom can significantly enhance the photoconversion efficiency by broadening the light absorption of the pristine g-C3N4 to visible light region. Our results highlight an interesting and experimentally synthesized single-atom photocatalyst (Pt@g-C3N4) for efficient hydrogenation of nitrobenzene to aniline under a sustainable and green approach.

Introduction

Hydrogenation is among the most important and challenging technological reactions in modern chemical industry [1]. The high activity and chemoselectivity are often very difficult to control especially when more than one reducible groups are present during the hydrogenation process [2, 3]. An important example is the catalytic hydrogenation of nitrobenzene into aniline, a high-value chemical raw material which can be widely used in dyes, pigments, rubber, agrochemical and pharmaceutical industry [4, 5]. Currently, the catalytic hydrogenation of nitro groups to produce anilines mainly relies on noble metal complexes catalysts, such as palladium, rhodium, ruthenium and iridium [6, 7]. Although the precious metals have the advantage of high catalytic activity, they still suffer from low selectivity and high expense. Therefore, the exploration of environmentally benign and cost effective catalysts for aniline synthesis is thus of great fundamental as well as practical interest [8–10]. Great research efforts toward improving the activity and selectivity has been made by developing a variety of catalysts: noble metal catalysts Au [9, 11, 12], AuPt [13], CoPd [14], Pd/CeO2 [2], non-noble metal catalysts Ni [15], Ni–Co as well as Ni–Fe alloys [16, 17] and so on [18–20]. However, the problem often arising is that these catalysts have to be modified by additives or combining with other metal oxides and molecules to achieve high selectivity [21–24]. In most cases, the well-chosen additives will cause environmental problems and at the same time reduce their activity [25].

Abstract

Persistent organic pollutants (POPs) are carbon-based chemical substances that are resistant to environmental degradation and may not be completely removed through treatment processes. Their persistence can contribute to adverse health impacts on wild-life and human beings. Thus, the solar photocatalysis process has received increasing attention due to its great potential as a green and eco-friendly process for the elimination of POPs to increase the security of clean water. In this context, ZnO nanostructures have been shown to be prominent photocatalyst candidates to be used in photodegradation owing to the facts that they are low-cost, non-toxic and more efficient in the absorption across a large fraction of the solar spectrum compared to TiO2. There are several aspects, however, need to be taken into consideration for further development. The purpose of this paper is to review the photo-degradation mechanisms of POPs and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnO as a photocatalyst. The second objective of this review is to evaluate the immobilization of photocatalyst and suspension systems while looking into their future challenges and prospects.

Introduction

In recent years, implementation of water reclamation and reuse is gaining attention rapidly world-wide due to the water scarcity occurred as a result of climate change and poor water resource management (i.e. limited access to clean water resources and water demands exceed the available resources). Access to clean water is becoming an ever increasing problem in an expanding global economy and population countries [1]. One of the attractive solutions in response to water issues is implementation of wastewater reclamation and reuse projects to ensure a sustainable water development and management. However, concerns still arise from the fact that persistent organic pollutants (POPs) could still be present in treated water.

The effect of H2 addition on CH4 decomposition over activated carbon (AC) catalyst was investigated. The results show that the addition of H2 to CH4 changes both methane conversion over AC and the properties of carbon deposits produced from methane decomposition. The initial methane conversion declines from 6.6% to 3.3% with the increasing H2 flowrate from 0 to 25 mL/min, while the methane conversion in steady stage increases first and then decreases with the flowrate of H2, and when the H2 flowrate is 10 mL/min, i.e. quarter flowrate of methane, the methane conversion over AC in steady stage is four times more than that without hydrogen addition. It seems that the activity and stability of catalyst are improved by the introduction of H2 to CH4 and the catalyst deactivation is restrained. Filamentous carbon is obtained when H2 is introduced into CH4 reaction gas compared with the agglomerate carbon without H2 addition. The formation of filamentous carbon on the surface of AC and slower decrease rate of surface area and pores volume may cause the stable activity of AC during methane decomposition. © 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Introduction

Hydrogen is a clean fuel and considered as an attractive alternative for fossil fuels and renewable energy sources. Generally, the main sources of hydrogen are fossil fuels, water, and methane, in which fossil fuels are also the main source of air pollution that causes considerable damage to the environment. Conventionally, most of the industrial hydrogen production is based on the steam methane reforming (SMR) process, however, large amount of carbon oxides as by-product leads to the increasing cost of hydrogen production because of the necessary purification process [1,2]. Electrochemical splitting of water is a process to produce hydrogen without COx emission, and some efficient catalysts have been developed to improve the efficiency of process and reduce the production cost [3e7]. Catalytic methane decomposition (CMD), another simple and promising process for production of hydrogen and carbon material without by-products CO and CO2, has received more and more attention. Many metal catalysts, such as Fe [8e10], Co [11e13] and Ni [14e16], were introduced into the process and proved as effective catalysts to promote methane decomposition. However, metal catalysts easily suffer the deactivation because the carbon deposition produced from methane encapsulates the surface active site of metals [17e19]. In comparison, carbon materials are considered as the alternative catalysts for methane decomposition to hydrogen owing to several advantages compared with metal catalysts such as low cost, high-temperature resistance, tolerance to sulfur and other potentially harmful impurities in the feedstock, and so on [20,21]. Activated carbon (AC) and carbon black are considered as more catalytically active materials than the more ordered ones such as graphite, diamond, carbon fibers and the carbon nanotubes [20,22], in which AC exhibits higher initial activity but lower sustainability. The rapid deactivation of AC catalysts is due to the blocking of the mouth of AC pores by growing carbon crystallites, which are generally in irregular agglomerate form [21,23]. Regeneration of carbon catalysts by carbonaceous deposit combustion with multiple cycles of reaction/regeneration or continuous supply of CO2/H2O to methane decomposition can effectively remove the carbon deposits and recover the carbon catalysts [24e26]. However, the regeneration of carbon catalysts will lead to the generation of undesirable COx and even destroy the catalyst itself [27]. The type of carbon deposition is confirmed to be an important factor to influence the activity of catalyst during methane decomposition [19].

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusions

References

Abstract

Here, we report the preparation of a Cr/ZrO2 composite catalyst for the reverse water-gas shift reaction (RWGS) that shows excellent low-temperature CO2 conversion and 100% CO selectivity. The catalyst was prepared from Cr-containing wastewater by photoreduction. Zirconia was used as a wide bandgap photocatalyst to photoreduce Cr(VI) under UV irradiation and immobilize the Cr species on the catalyst surface, resulting in a high dispersion. The results show that the obtained 1 wt%Cr/ZrO2 can catalyze the RWGS to reach the thermodynamic limit at 600 °C. The CO yield at 600 °C with photoreduced Cr/ZrO2 after calcination, 38.34%, is significantly higher than that of the catalyst prepared by impregnation. Metal hydrides were determined to be the key intermediates in the RWGS reaction with Cr/ZrO2 as the catalyst, and the cyclic conversion between Cr(VI) and Cr(III) caused by the hydrogen reduction and CO2 oxidation improves the catalytic activity. This study provides a strategy to acquire a promising RWGS catalyst for CO2 emission reduction and utilization and an attractive method to treat Cr-containing wastewater.

Introduction

Carbon dioxide hydrogenation is an effective strategy for CO2 emission reduction and utilization[1], and the reverse water-gas shift reaction (RWGS) is an attractive and promising route[2] for this process with industrial value. CO2 is typically inert but can be activated and converted into valuable CO with low hydrogen consumption in the RWGS. The CO can be used for further production with value-added products such as methanol[3] in the CAMERE (Carbon Dioxide Hydrogenation to Form Methanol via a Reverse-Water-Gas-Shift Reaction) process and alkenes[4] in alkane oxidative dehydrogenation. As a typical endothermic reaction, the RWGS reaction enthalpy is 42.1 kJ mol-1 . Thus, the most favorable reaction conditions involve high temperatures and a high ratio of hydrogen to CO2 for reaction conversion enhancement. However, the high reaction temperatures result in high energy consumption and rapid catalyst deactivation because of severe carbon deposition, as well as competitive methanation side reactions. A high hydrogen-to-carbon ratio increases the operating costs and makes it difficult to adjust the proper hydrogen-carbon ratio for follow-up production. Thus, the development of a catalyst with excellent low-temperature activity and good anti-coking capability with a low hydrogen-to-carbon ratio for the RWGS was investigated.

Nanostructured materials have attracted great interest because of their tunable structures and broad applications [1–5]. Among variable nanostructures, the development of porous nanostructures is an important research area because of their unique physicochemical properties and applicability such as for adsorption, biomedicine, chromatography, catalysis, energy convergence, and gas storage [6–10]. Variable porous nanostructured materials have been applied in catalysis research areas for elevating the efficiency of the catalytic transformations [11–14]. For instance, mesoporous silica and alumina materials have been used as supports for precious nanoparticles (NPs) catalysts due to their low cost, large surface area and porosity, chemical and thermal stability, mechanical strength, and simple synthesis [15–17]. Mesoporous inorganic materials that supported palladium NPs catalysts have expedited various important reactions [18–20]. Another interesting feature of mesoporous silica is the multitude of possible modifications that can be used for easy organics functionalization to present the desired properties [21, 22]. Mesoporous silica materials functionalized with acidic groups (e.g., –COOH, – SO3H, –SH) and/or basic groups (e.g., –NH2, –NRH, –NR2) have been utilized as non-metallic solid catalysts in various reactions such as cascade reactions [23–25]. These heterogeneous catalysts have the benefits of simple recovery and reuse after the accomplishment of reactions and present green chemical processes in comparison to their homogeneous counterparts [26–28]. Although great efforts have been achieved to develop highly stable and sustainable solid acid/base catalysts, there are still major deficiencies with most matrixes needing rectification including available active catalytic sites, catalytic efficiency, and substrates diffusion [29, 30]. In addition, reactants adsorption and interaction with the functional groups in small pore-size supports restrict the effectiveness of these heterogeneous catalysts [31].