Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Selective catalytic reduction with NH3 (NH3-SCR) is the most efficient technology to reduce the emission of nitrogen oxides (NOx) from coal-fired industries, diesel engines, etc. Although V2O5-WO3(MoO3)/TiO2 and CHA structured zeolite catalysts have been utilized in commercial applications, the increasing requirements for broad working temperature window, strong SO2/alkali/heavy metal-resistance, and high hydrothermal stability have stimulated the development of new-type NH3-SCR catalysts. This review summarizes the latest SCR reaction mechanisms and emerging poison-resistant mechanisms in the beginning and subsequently gives a comprehensive overview of newly developed SCR catalysts, including metal oxide catalysts ranging from VOx, MnOx, CeO2, and Fe2O3 to CuO based catalysts; acidic compound catalysts containing vanadate, phosphate and sulfate catalysts; ion exchanged zeolite catalysts such as Fe, Cu, Mn, etc. exchanged zeolite catalysts; monolith catalysts including extruded, washcoated, and metal-mesh/foam-based monolith catalysts. The challenges and opportunities for each type of catalysts are proposed while the effective strategies are summarized for enhancing the acidity/redox circle and poison-resistance through modification, creating novel nanostructures, exposing specific crystalline planes, constructing protective/sacrificial sites, etc. Some suggestions are given about future research directions that efforts should be made in. Hopefully, this review can bridge the gap between newly developed catalysts and practical requirements to realize their commercial applications in the near future.

Selective Catalytic Reduction of NOx with NH3 by Using Novel Catalysts: State of the Art and Future Prospects.

Anaerobic digestion of food waste - Challenges and opportunities.

Globally, there is increasing awareness that renewable energy and energy efficiency are vital for both creating new economic opportunities and controlling the environmental pollution. AD technology is the biochemical process of biogas production which can change the complex organic materials into a clean and renewable source of energy. AcoD process is a reliable alternative option to resolve the disadvantages of single substrate digestion system related to substrate characteristics and system optimization. This paper reviewed the research progress and challenges of AcoD technology, and the contribution of different techniques in biogas production engineering. As the applicability and demand of the AcoD technology increases, the complexity of the system becomes increased, and the characterization of organic materials becomes volatile which requires advanced methods for investigation. Numerous publications have been noted that ADM1 model and its modified version becomes the most powerful tool to optimize the AcoD process of biogas production, and indicating that the disintegration and hydrolysis steps are the limiting factors of co-digestion process. Biochemical methane potential (BMP) test is promising method to determine the biodegradability and decomposition rate of organic materials. The addition of different environmentally friendly nanoparticles can improve the stability and performance of the AcoD system. The process optimization and improvement of biogas production still seek further investigations. Furthermore, using advanced simulation approaches and characterization methods of organic wastes can accelerate the transformation to industrializations, and realize the significant improvement of biogas production as a renewable source and economically feasible energy in developing countries, like China. Finally, the review reveals, designing and developing a framework, including various aspects to improve the biogas production is essential.

Anaerobic co-digestion process for biogas production: Progress, challenges and perspectives

Food waste generation and industrial uses: A review.

The biochemical methane potentials for typical fruit and vegetable waste (FVW) and food waste (FW) from a northern China city were investigated, which were 0.30, 0.56 m3 CH4/kgVS (volatile solids) with biodegradabilities of 59.3% and 83.6%, respectively. Individual anaerobic digestion testes of FVW and FW we re conducted at the organic loading rate (OLR) of 3 k g VS/(m3.day) using a lab-scale continuous stirred-tank reactor at 350C. FVW could b e digested stably with the biogas production rate of 2.17 m3/(m3 .day)and methane production yield of 0.42 m3 CH4/kg VS. However, anaerobic digestion process for FW was failed due to acids accumulation. The effects of FVW: FW ratio on co-digestion stability and performance were further investigated at the same OLR. At FVW and FW mixing ratios of 2:1 and 1:1, the performance and operation of the digester were maintained stable, with no accumulation of volatile fatty acids (VFA) and ammonia. Changing the feed to a higher FW content in a ratio of FVW to FW 1:2, resulted in an increase inVFAs concentration to 1100-1200 mg/L, and the methanogenesis was slightly inhibited. At the optimum mixture ratio 1:1 for co-digestion of FVW with FW, the methane production yield was 0.49 m3 CH4/kg VS, and the volatile solids and soluble chemical oxygen demand (sCOD) removal efficiencies were 74.9% and 96.1%, respectively.

Effects of mixture ratio on anaerobic co-digestion with fruit and vegetable waste and food waste of China.

A CuO–CeO2–TiO2 catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures was prepared by a sol–gel method and characterized by X-ray diffraction, Brunner–Emmett–Teller surface area, ultraviolet–visible spectroscopy, H2 temperature-programmed reduction, scanning electron microscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The CuO–CeO2–TiO2 ternary oxide catalyst shows excellent NH3-SCR activity in a low-temperature range of 150–250 °C. Lewis acid sites generated from Cu2+ are the main active sites for ammonia activation at low temperature, which is crucial for low temperature NH3-SCR activity. The introduction of ceria results in increased reducibility of CuO species and strong interactions between CuO particles with the matrix. The interactions between copper, cerium and titanium oxides lead to high dispersion of metal oxides with increased active oxygen and enhanced catalyst acidity. Homogeneously mixed metal oxides facilita...

DRIFT Study of CuO–CeO2–TiO2 Mixed Oxides for NOx Reduction with NH3 at Low Temperatures

A zirconium phosphate @ Ce 0.75 Zr 0.25 O 2 (ZP/CZ) catalyst was synthesized by impregnating zirconium phosphates on Ce 0.75 Zr 0.25 O 2 microspheres. Catalysts with different structures were also synthesized by various methods to illustrate the structure advantage of ZP/CZ catalyst in selective catalytic reduction of NO x by ammonia (NH 3 -SCR). The catalysts were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), BET surface area, Infrared (IR) spectra, Ultraviolet-visible (UV–vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), H 2 -temperature programmed reduction (TPR) and diffuse reflectance infrared Fourier transformed spectra (DRIFTS) of NH 3 /NO x adsorption. ZP/CZ catalyst presents excellent catalytic activity at 250–450 °C with a good N 2 selectivity under high space velocity of 300,000 h −1 . Firstly, the zirconium phosphate provides adsorption sites for ammonia on the surface of the catalyst and the cerium sites in the core act as the redox sites for NO oxidation. The pre-combination of zirconium and phosphate can reduce the strong interactions between phosphates and cerium ions. Therefore, the mobility of surface lattice oxygen on Ce 0.75 Zr 0.25 O 2 catalyst is retained, which is essential to obtain a catalyst with high NH 3 -SCR activity at low temperatures. Moreover, NH 4 NO 3 has proved to be an important intermediate for the NH 3 -SCR reaction on the surface of ceria based catalysts. The ZP/CZ catalyst preserves plenty of oxygen vacancies, facilitating the Ce 4+  → Ce 3+ redox circles and therefore promotes the nitrites/nitrates formation and desorption on catalyst. Two distinct adsorption sites for NH 3 and NO x result in a close contact between ads-NH 3 /NH 4 + and ads-NO 3 − /NO 2 − species on ZP/CZ catalyst, which can react with NO rapidly with the participation of active surface lattice oxygen.

Lei Chen

Papers

Effects of mixture ratio on anaerobic co-digestion with fruit and vegetable waste and food waste of China.

DRIFT Study of CuO–CeO2–TiO2 Mixed Oxides for NOx Reduction with NH3 at Low Temperatures

Selective catalytic reduction of NOx by ammonia over phosphate-containing Ce0.75Zr0.25O2 solids

Formation of FeOOH Nanosheets Induces Substitutional Doping of CeO2−x with High-Valence Ni for Efficient Water Oxidation

Synergistic effect between ceria and tungsten oxide on WO3–CeO2–TiO2 catalysts for NH3-SCR reaction