Recent advances in zeolite-encapsulated metal catalysts: a suitable catalyst design for catalytic biomass conversion

Metal clusters and nanoparticles, which have been used to tune the acidity of zeolite support, are beneficial for promoting the catalytic performance of various reaction processes, including biomass conversion. However, catalytic instabilities resulting from metal coalescence, sintering and leaching are major problems that need to be resolved. Therefore, metal encapsulation within the zeolite structure has been proposed as a feasible solution for this issue, particularly for biomass conversions that require high temperatures. In this current review, recent developments in metal confinement techniques are described along with experimental examples of biomass upgrading reactions. The present and future perspectives of zeolite-encapsulated metal catalysts in biomass conversions are also given

A Review on the Production and Purification of Biomass-Derived Hydrogen Using Emerging Membrane Technologies

Hydrogen energy systems are recognized as a promising solution for the energy shortage and environmental pollution crises. To meet the increasing demand for hydrogen, various possible systems have been investigated for the production of hydrogen by efficient and economical processes. Because of its advantages of being renewable and environmentally friendly, biomass processing has the potential to become the major hydrogen production route in the future. Membrane technology provides an efficient and cost-effective solution for hydrogen separation and greenhouse gas capture in biomass processing. In this review, the future prospects of using gas separation membranes for hydrogen production in biomass processing are extensively addressed from two perspectives: (1) the current development status of hydrogen separation membranes made of different materials and (2) the feasibility of using these membranes for practical applications in biomass-derived hydrogen production. Different types of hydrogen separation membranes, including polymeric membranes, dense metal membranes, microporous membranes (zeolite, metal-organic frameworks (MOFs), silica, etc.) are systematically discussed in terms of their fabrication methods, gas permeation performance, structure stability properties, etc. In addition, the application feasibility of these membranes in biomass processing is assessed from both practical and economic perspectives. The benefits and possibilities of using membrane reactors for hydrogen production in biomass processing are also discussed. Lastly, we summarize the limitations of the currently available hydrogen membranes as well as the gaps between research achievements and industrial application. We also propose expected research directions for the future development of hydrogen gas membrane technology

Metal encapsulation in zeolite particles: a rational design of zeolite-supported catalyst with maximum site activity

Zeolite-supported metal catalysts have been proven effective in many important catalytic reactions, such as hydrogenation, Fisher-Tropsch synthesis, automobile exhaust catalysis, selective catalytic reduction and many others. Despite the successful preparation of the catalyst through widely adopted methods, including ion exchange and impregnation, the metal dispersion over the zeolite is lack of control with high randomness. This renders the so-called “catalytic performance” an overall contribution from the metal sites located inside the zeolite micropores and those located on the external surface. This is exceptionally true for small to medium pore zeolites with typical free apertures of 0.3 – 0.6 nm (such as LTA and MFI). A more rational design of zeolite-supported metal catalysts is by encapsulating the metal nanoparticles or clusters within zeolite pores prior to the zeolite formation. Encapsulation of metals in zeolite prevents them from sintering and sulphur poisoning by cage confinement and molecular exclusion (via well-defined pore size and shape), respectively. This paper gives a new perspective on using metal clusters and nanoparticles as catalysts and the design of an effective zeolite-supported catalytic system

Chemical-vapor-deposited copper on acid-activated bentonite clay as an applicable heterogeneous catalyst for the photo-fenton-like oxidation of textile organic pollutants

A heterogeneous Cu/clay catalyst was synthesized by dispersing copper onto the surface of bentonite clay through chemical vapor deposition (CVD). To resolve the copper leaching problem during the catalyst's application in aqueous reaction, a critical pretreatment step, acid activation by H2SO 4, was applied to the original bentonite clay. Such manufactured Cu/clay catalyst was characterized and evaluated in the photo-Fenton-like degradation of an azo organic dye, Acid Black l (AB1). It was found that the acid activation process of clay could significantly reduce the leaching problem by almost 72% and improve the catalytic activity. These improvements came from the active site and the addition of sulfonate functional group on the clay surface. It was also observed that the adsorption and desorption properties of the Cu/acid-activated clay play an important role in the catalytic reaction and that its catalytic performance is better than Fe/clay at pH 7 and 9. It also has a comparable activity to that of Fe/clay at pH 3. This advantage increases the potential of the catalyst in the treatment of organic contaminated wastewater. The optimum reaction conditions in a 1-L reactor equipped with 8 W UVC light were determined to be 0.1 mM AB1, 6.4 mM H2O2, 0.5 g/L catalyst loading, pH 3, at ambient temperature of 30°C. It was also found that splitting the required dosage of H2O2 could minimize the H2O2 scavenging effect and results in a higher total organic carbon (TOC) removal. © 2005 American Chemical Society.link_to_subscribed_fulltex

A novel heterogeneous acid-activated clay supported copper catalyst for the photobleaching and degradation of textile organic pollutant using photo-Fenton-like reaction

Copper supported on acid-activated bentonite clay was found to be an effective catalyst for the photo degradation of Acid Black 1 at pH 3.0-8.0 without significant metal leaching

Advances in the Green Synthesis of Microporous and Hierarchical Zeolites: A Short Review

Hierarchical zeolites have been extensively studied due to their enhancement of intra-crystalline diffusion, which leads to the improved catalytic activity and resistance to coking-deactivation. Traditional synthesis strategies of hierarchical zeolites via post-treatment or directing synthesis with the aid of mesoporous template are often characterized by high energy consumption and substantial use of expensive and environmentally unfriendly organic templates. In the recent decade, new green synthesis protocols have been developed for the effective synthesis of conventional and hierarchical zeolites. In this review, the latest advancements on the green synthesis of hierarchical zeolites are summarized and discussed in detail

A heterostructured titanium silicalite-1 catalytic composite for cyclohexanone ammoximation

Submicron-sized titanium silicalite-1 is difficult to recover in industrial process because of their fineness and rapid decrease in catalytic activity due to particle agglomeration. To solve these problems, we present a heterostructured titanium silicalite-1 (TS-1) catalytic composite using bentonite clay as the catalyst support. The catalytic composite is synthesized by hydrothermal treatment which directly crystallizes TS-1 on the bentonite clay surface. The synthesized composite has been characterized using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TS-1 crystals have been found on and between the layers of the bentonite with strong attachment. Characterizations suggest that crystallization temperature of 175 °C is the optimum hydrothermal temperature to produce TS-1 on the bentonite support with characteristics necessary to promote selective catalytic reactions. It is found that prolonged crystallization duration does not necessarily increase the crystallinity of TS-1 on the bentonite surface. The heterostructured composite is able to maintain high conversion of cyclohexanone (97%) and oxime selectivity (83%) after three reaction cycles which is contrary to the unsupported TS-1 that shows apparent decrease in activity (>10%), especially in the selectivity to oxime. The synthesized composite also has significant improvement in separation efficiency with respect to the unsupported catalytic system. Therefore, we conclude that the heterostructured TS-1 composite is a promising catalytic material for cyclohexanone ammoximation and potentially for other TS-1 related processes where catalyst recovery and reuse are required. © 2008 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex

Copper/MCM-41 as a highly stable and pH-insensitive heterogeneous photo-fenton-like catalytic material for the abatement of organic wastewater

A heterogeneous catalyst was synthesized by supporting copper metal on MCM-41 by chemical vapor deposition (CVD). The usage of oxygen as a carrier gas and oxidizing agent is found to be very important in producing a stable and effective Cu/MCM-41 catalyst. This MCM-41-supported copper catalyst is evaluated in the photo-Fenton-like degradation of a dye pollutant, Orange II. Results show that the Cu/MCM-41 catalyst is effective in mineralizing total organic carbon (TOC) of 80%, 78%, and 70% at pH 3, 5.5, and 7, respectively, successfully overcoming the low efficiency problem of the conventional Fenton reaction at high pH. Moreover, the synthesized catalyst is proved to be durable with a stable TOC removal efficiency after four consecutive cycles. The kinetic study of pollutant degradation using Cu/MCM-41 is also conducted. © 2007 American Chemical Society.link_to_subscribed_fulltex