As a promising approach for carbon dioxide capture, chemical looping combustion has been extensively investigated for more than two decades. However, the chemical looping strategy can be and has been extended well beyond carbon capture. In fact, significant impacts on emission reduction, energy conservation, and value-creation can be anticipated from chemical looping beyond combustion (CLBC). This article aims to demonstrate the versatility and transformational benefits of CLBC. Specifically, we focus on the use of oxygen carriers or redox catalysts for chemical production – a $4 trillion industry that consumes 40.9 quadrillion BTU of energy. Compared to state-of-the-art chemical production technologies, we illustrate that chemical looping offers significant opportunities for process intensification and exergy loss minimization. In many cases, an order of magnitude reduction in energy consumption and CO2 emission can be realized without the needs for carbon dioxide capture. In addition to providing various CLBC examples, this article elaborates on generalized design principles for CLBC, potential benefits and pitfalls, as well as redox catalyst selection, design, optimization, and redox reaction mechanism.

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Chemical looping beyond combustion – a perspective

The most widely used catalysts and processes for H2S-selective catalytic oxidation are overviewed in this review. Two kinds of catalysts have been investigated intensively: carbon-based catalysts (active carbon catalyst, carbon nanotube catalyst, and carbon nanofiber catalyst), metal oxide-based catalysts (metal oxide catalyst, oxide-supported catalyst, and clay-supported catalyst). Among them, carbon-based catalysts are utilized mainly in discontinuous processes at relatively low temperatures, whereas metal oxide catalysts are the most widely used in practice. However, the reaction temperature is relatively high. Fortunately, a MgAlVO catalyst derived from LDH materials and intercalated clay-supported catalysts exhibit excellent catalytic activities at relatively lower temperatures. According to various studies, the catalytic behaviors mainly obey the Mars–van Krevelen mechanism; however, the catalyst deactivation mechanism differs, depending on the catalyst. In practice, the mobil direct oxidation proce...

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H2S-Selective Catalytic Oxidation: Catalysts and Processes

Efficient construction of bismuth vanadate-based Z-scheme photocatalyst for simultaneous Cr(VI) reduction and ciprofloxacin oxidation under visible light: Kinetics, degradation pathways and mechanism

Harvesting clean energy from fuel feedstocks is of paramount significance in the field of environmental science. In this dynamic area, desulfurization provides a valuable contribution by eliminating sulfur compounds from fuel feedstocks to ensure the utilization of fuels without the emission of toxic sulfur oxides (SOx gases). Nonetheless, the inadequacy of the current industrial technique (hydrodesulfurization, HDS) in the removal of refractory sulfur (RS) compounds and the stringent rules imposed on the fuel sulfur level have kindled research on other desulfurization methods like oxidative desulfurization (ODS). With the capacity of eliminating RS compounds under mild conditions, ODS is endorsed as a suitable replacement or complementary to HDS. ODS, in general, consists of two steps: (i) oxidation and (ii) extraction. The oxidation of sulfur compounds is carried out using a suitable catalyst (hereafter termed as an ODS catalyst) in the presence of an oxidant. Choosing a suitable ODS catalyst for industrial applications is still a quest among the various types of catalysts reported so far. With this outline, herein, all the types of ODS catalysts along with their synthetic methods, reactivity and mechanistic insights are reviewed. The activity of ODS catalysts could be influenced by factors like the type of RS compound, solvent, fuel, etc. and those factors are reviewed. The effects of ionic liquids, light, and ultrasound on the performance of ODS catalysts are also briefly summarized. The opportunities and challenges for ODS catalysts are comprehensively explicated in the end. Through this review, systematic information about the types of ODS catalysts including the basic definition, preparative methods, reactivity and mechanism can be comprehended. Furthermore, this review reveals the merits and demerits related to highlighting catalytic ODS as a replacement or complementary to HDS.

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A comprehensive review on oxidative desulfurization catalysts targeting clean energy and environment

Shape-specific CeO2 nanocrystals (rods, cubes, spheres and nanoparticles) with well-defined crystal facets and hierarchically porous structure were successfully synthesized and used as model catalysts to study the structure-dependent behavior and reaction mechanism for H2S selective oxidation over ceria-based catalysts. It is deduced that the defect sites and base properties of CeO2 are intrinsically determined by the surface crystal facets. Among the nanocrystals, CeO2 nanorods with well-defined {110} and {100} crystal facets exhibits superb catalytic activity and sulfur selectivity. The high reactivity for H2S selective oxidation is attributed to the high concentration of surface oxygen vacancies which are beneficial for the conversion of lattice oxygen to active oxygen species. Besides, the presence of hierarchically porous structure of CeO2 nanorods hinders the formation of SO2 and sulfate, ensuring good sulfur selectivity and catalyst stability. Through a combined approach of density-functional theory (DFT) calculations and in situ DRIFTS investigation, the plausible reaction mechanism and nature of active sites for H2S selective oxidation over CeO2 catalysts have been revealed.

Insight into the effect of morphology on catalytic performance of porous CeO2 nanocrystals for H2S selective oxidation

With the increasing of bacterial resistance to available antibiotics and water contamination by poisonous organic dyes, it’s necessary to consider how to overcome these concerns. In this paper, novel visible-light-sensitive InVO 4 /AgVO 3 photocatalysts with a p - n junction were synthesized through an ion exchange and in-situ growth process. The obtained photocatalysts were characterized by X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (UV-DRS) respectively. It can be observed that the AgVO 3 exhibits a rod-shaped structure, while a plentiful of spherical shaped InVO 4 particles are formed on the surface. The rod-shaped structure of AgVO 3 wasn’t changed by the addition of InVO 4 , but its photocatalytic properties were tremendously improved. The best photocatalyst was 0.5InVO 4 /AgVO 3 , over which the Rhodamine B (RhB) solution was almost decomposed in 200 min under visible light irradiation. Moreover, about 99.9999% of P. aeruginosaudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were killed over 0.5InVO 4 /AgVO 3 at 30 min. From these results it can be inferred that 0.5InVO 4 /AgVO 3 heterojunctional photocatalyst has an improved efficiency for the separation of the current carriers to enhance the photocatalytic performances. This result provided a valuable design for the novel InVO 4 /AgVO 3 heterojunction photocatalysts with excellent photocatalytic properties used in marine antifouling.

Fabrication of InVO4/AgVO3 heterojunctions with enhanced photocatalytic antifouling efficiency under visible-light

H2S selective catalytic oxidation over Ce substituted La1−xCexFeO3 perovskite oxides catalyst

A series of Mg2AlxV1–x–LDH (LDH = layered double hydroxide) was synthesized by using a facile method, and well-mixed derived oxides were obtained after calcinations. These catalysts were further tested for H2S selective oxidation. Meanwhile, the physicochemical properties of the catalysts were investigated by various methods. It was observed that vanadium species existed mainly in the form of isolated V5+ in distorted [VO4],Mg3V2O8 and VO2+. Significantly, these catalysts exhibited high catalytic activities in a relatively lower range of reaction temperatures (100–200 °C) as a result of the well-dispersed vanadium species and excellent moderate basicity property. A catalytic reaction mechanism was proposed as follows: H2S was first adsorbed on the Mg–O–Mg band of MgO (moderate basic sites), forming S2– and H2O, then the S2– was oxidized to Sn by V5+, simultaneously, forming oxygen vacancies and V4+. Finally, V4+ was oxidized to V5+ by O2, and O2– was incorporated into oxygen vacancies. In addition, the ca...

Selective Catalytic Oxidation of H2S over Well-Mixed Oxides Derived from Mg2AlxV1–x Layered Double Hydroxides

MnxAlO mixed oxide catalysts derived from MnxAl-LDHs were prepared and tested for acetone catalytic oxidation. Detailed results indicated that the surface intrinsic and formed oxygen vacancies can induce the Mn-O bond of structural unit [MnO6] weakened. Subsequently, it can improve the redox properties of catalysts, and enhance the capacity of gaseous oxygen species dissociation and adsorption. Among them, Mn3AlO catalyst displayed the best catalytic performance for acetone oxidation (T90 = 164 °C) with the production of low amount of byproduct ( 99%) producted. Additionally, the Mn3AlO catalyst can proceed consecutively for 12 h reaction without notable deactivation. Furthermore, in situ DRIFT and theoretical calculations methods was adopted to explore the reaction mechanism. And η1(O)(ads) (adsorption mode of acetone), CH2=C(CH3)=O(ads), O*, CH3CHO*, CH2O* and COO(ads) were considered as the main intermediate species and/or transient state during the reaction process. It was revealed that the acetone and oxygen molecules were activated by the dehydrogenation (α-H abstraction) and dissociation process over Mn3AlO catalyst, respectively, and then the intermediate specie, CH2 C(CH3) O and O*, were produced, which was followed by the breaking of C C bonds to produce the CH3CHO* and CH2O* species. Finally, these species were attacked by dissociated oxygen (O*) and therefore further dehydrogenation occurred, form H2O and CO2 via the COO adsorbed species. Particularly, C C bond breaking was the main rate determining step for acetone oxidation.

Surface properties enhanced MnxAlO oxide catalysts derived from MnxAl layered double hydroxides for acetone catalytic oxidation at low temperature

A series of Mg2Al-V10O28-LDH (named V-LDH) were synthesized using ion-exchange method, and the derived oxides were investigated for H2S selective oxidation. The physicochemical properties of the catalysts were assessed by various methods. It was observed that vanadium species existed mainly in the form of isolated V5+ in distorted [VO4], Mg3V2O8, and Mg2V2O7. Moreover, there was a large amount of V4+ species (>25%), mainly formed with vanadyl bonds. Significantly, the catalysts exhibited excellent catalytic performances at relatively low reaction temperatures (100-200 degrees C). Furthermore, the catalyst containing 10.6 wt% vanadium (8V-LDO) was highly durable at a relatively low temperature (160 degrees C) and a high gas hourly space velocity (GHSV, 24,000 h(-1)), which can proceed consecutively for 100 h without notable deactivation. In the reaction process, the gradually produced sulfate species reacted with V4+ species to form less active VOSO4 species, which improved the redox property of V5+. The catalysts obeyed a step-wise mechanism for H2S selective catalytic oxidation. The excellent durability can be ascribed to the fact that the content of moderate basic sites was kept and the redox property of V5+ was improved. (C) 2015 Elsevier B.V. All rights reserved.

Xin Zhang

Papers

Fabrication of InVO4/AgVO3 heterojunctions with enhanced photocatalytic antifouling efficiency under visible-light

H2S selective catalytic oxidation over Ce substituted La1−xCexFeO3 perovskite oxides catalyst

Selective Catalytic Oxidation of H2S over Well-Mixed Oxides Derived from Mg2AlxV1–x Layered Double Hydroxides

Surface properties enhanced MnxAlO oxide catalysts derived from MnxAl layered double hydroxides for acetone catalytic oxidation at low temperature

Comprehensive study of H2S selective catalytic oxidation on combined oxides derived from Mg/Al-V10O28 layered double hydroxides