Yongdan Li

Catalytic Ethanolysis of Kraft Lignin into High-Value Small-Molecular Chemicals over a Nanostructured α-Molybdenum Carbide Catalyst†

We report the complete ethanolysis of Kraft lignin over an α-MoC1-x /AC catalyst in pure ethanol at 280 °C to give high-value chemicals of low molecular weight with a maximum overall yield of the 25 most abundant liquid products (LP25) of 1.64 g per gram of lignin. The LP25 products consisted of C6 -C10 esters, alcohols, arenes, phenols, and benzyl alcohols with an overall heating value of 36.5 MJ kg(-1) . C6 alcohols and C8 esters predominated and accounted for 82 wt % of the LP25 products. No oligomers or char were formed in the process. With our catalyst, ethanol is the only effective solvent for the reaction. Supercritical ethanol on its own degrades Kraft lignin into a mixture of small molecules and molecular fragments of intermediate size with molecular weights in the range 700-1400, differing in steps of 58 units, which is the weight of the branched-chain linkage C3 H6 O in lignin. Hydrogen was found to have a negative effect on the formation of the low-molecular-weight products.

Measurement and statistics of single pellet mechanical strength of differently shaped catalysts

Mechanical-strength measurement methods for differently shaped solid catalysts, such as crushing, knife-edge cutting and three-point bending have been discussed. The strength data were correlated by Weibull distribution. Experimental results show that, except for the crushing strength test on extruded catalysts, all strength tests have a single fracture mode, and the strength failures are due to brittle fracture, originating from tensile stress concentration at the edges of the existing flaws in the catalyst pellets. The suitability of different test methods for spheres, tablets and extrudates, respectively, are discussed. It is concluded that the crushing test is a satisfactory method for spheres, and crushing and cutting tests are both suitable for tablets, while cutting and bending tests are appropriate for extrudates.

Catalytic growth of carbon fibers from methane on a nickel-alumina composite catalyst prepared from Feitknecht compound precursor

Abstract A nickel-alumina catalyst prepared from Feitknecht compound was used in the catalytic growth of carbon fibers from methane. An in situ thermal balance was employed in the study of the reaction and in the TPR of the oxide precursors. A number of catalysts from the same structure with different nickel to aluminum ratios were tested, for comparison with a nickel oxide also prepared by precipitation. All the samples containing aluminum exhibited high activity at a low temperature, yet the nickel oxide had no activity under the same conditions. It has been observed that, as the Ni/Al ratio increases, the crystallinity of the Feitknecht compound decreases. However, the amount of the carbon fiber formed before the deactivation of the catalyst is proportional to the amount of the nickel in the catalyst. The reduction and the reaction temperatures both have strong effects on the reaction. A small amount of hydrogen in the feed retards fibers formation. At 773 K, the weight of carbon fiber formed on one of the catalysts attained 85 times that of the original unreduced catalyst in the cofeeding of methane and nitrogen. SEM and TEM photographs showed that the carbon fibers formed winding tubes, and their diameters were in the range of 15–69 nm. The shape of the break sections and the existence of dislocations in the fibers suggest that the fibers formed in this work are in accord with the fishbone structure model.

Biphasic Hydrogenation over PVP Stabilized Rh Nanoparticles in Hydroxyl Functionalized Ionic Liquids

Polyvinyl pyrrolidone stabilized rhodium nanoparticles are highly soluble in hydroxyl-functionalized ionic liquids, providing an effective and highly stable catalytic system. In hydrogenation reactions, excellent results were obtained, and transmission electron microscopy, solubility determinations, and leaching experiments were employed to quantify the advantages of this catalytic system.

An efficient catalytic dehydration of fructose and sucrose to 5-hydroxymethylfurfural with protic ionic liquids.

The renewable furan-based platform chemical, 5-hydroxymethylfurfural (HMF), has been efficiently synthesized from d-fructose and sucrose in the presence of a catalytic amount of protic ionic liquids. The 1-methylimidazolium-based and N-methylmorpholinium-based ionic liquids are employed. As a result, 74.8% and 47.5% yields of HMF are obtained from d-fructose and sucrose, respectively, at 90 degrees C for 2h under nitrogen atmosphere when N-methylmorpholinium methyl sulfonate ([NMM](+)[CH(3)SO(3)](-)) is used as the catalyst in an N,N-dimethylformamide-lithium bromide (DMF-LiBr) system. The acidities of ionic liquids are determined by the Hammett method, and the correlation between acidity and catalytic activity is discussed. Moreover, the effects of reaction temperature and time are investigated, and a plausible reaction mechanism for the dehydration of d-fructose is proposed.

Formation of bamboo-shaped carbon filaments and dependence of their morphology on catalyst composition and reaction conditions

Abstract Carbon filaments and nanometric carbon particles formed from methane on nano-sized Ni–Cu/Al2O3 catalyst at 720–830°C were investigated with a transmission electron microscope. Bamboo-shaped carbon filaments were found formed at moderate temperatures. Their morphology depends on the amount of copper doped into the catalyst, the composition of the feed gas and the reaction temperature. Under appropriate conditions, a morphologically pure bamboo-shaped carbon filament can be produced. It is likely that the formation of the quasi-liquid state of the metal nanoparticles during the growth of the carbon is critical for the formation of bamboo shape. The sensitivity of the carbon morphologies to the nano-carbon to the characteristics of catalyst and reaction conditions provides some room for the nanosize construction with carbon under moderate catalytic conditions.

Catalytic synthesized carbon nanostructures from methane using nanocrystalline Ni

Abstract Carbon nanostructures synthesized with nanocrystalline Ni catalyst from decomposition of methane are investigated by means of transmission electron microscopy (TEM). Two kinds of carbon nanostructures, carbon fibers and bamboo-shaped carbon nanotubes, are observed. The preferential growth direction of graphene sheets depends on the reaction conditions. The bamboo-shaped carbon nanotubes can be obtained only if the reaction temperature is higher than 1000 K, and carbon fibers can be obtained at lower temperatures. The role and state of the catalyst particles are also discussed.

A Review on the Pd-Based Three-Way Catalyst

The application of Pd in three-way catalyst represents a significant technology breakthrough for the removal of pollutants from gasoline powered vehicle exhaust gas. Pd shows superior catalytic activity for hydrocarbon (HCs) oxidation and thermal stability to the conventional Pt/Rh catalyst. However, Pd catalysts are more susceptible to chemical poisoning. This work summarizes the progress of the Pd-based three-way catalyst and its related technologies. The state of Pd in the reaction, the support and oxygen storage material, the promoters, and preparation methods on the catalytic performance are reviewed. The process and catalyst configurations, e.g., close-couple (CCC), dual bricks, layered, and zone-coated catalysts, are described and compared. The advances in the understanding of the reaction and deactivation mechanisms in the three-way catalysis systems are also discussed.

Effects of the number of testing specimens and the estimation methods on the Weibull parameters of solid catalysts

Abstract A Monte Carlo simulation is used to obtain the statistical properties of the Weibull parameters estimated by the linear regression, weighted linear regression and maximum likelihood schemes, respectively. Results reveal that the natural logarithm of the Weibull size parameter can be determined with about the same precision as the Weibull modulus. For Weibull modulus estimation, a maximum likelihood method results in the highest estimation precision; however, with a low safety factor. The weighted linear regression method with a weight factor Wi=Fi2 and a probability estimator Pf(Fi)=(i−0.3)/(n+0.4) or Pf(Fi)=(i−3/8)/(n+1/4), which leads to a similar estimation precision and a much higher safety factor, is considered to be the best method for engineering design. Simulations show that the weight factors and the probability estimators have effects on the estimation precision. It is also concluded that the precision of any estimation method increases with the increase of the sample size. It is reaffirmed that 30–60 specimens are required to obtain a reasonable estimation precision of the Weibull parameters.

Understandings on the scattering property of the mechanical strength data of solid catalysts - A statistical analysis of iron-based high-temperature water-gas shift catalysts

Abstract Statistics reveal that horizontal crushing strength data scatter in rather large ranges for cylindrical iron-based high-temperature water-gas shift catalyst tablets. This scattering is due to brittle fracture nature of the strength failure, originating from the stress concentration around edges of existing micro-cracks, such as pores, defects, and discontinuations contained in tablets. However, variations in the tablet size and density are found to contribute to strength data scattering. Data of tablet strength, height and density of the catalysts are found to be scattered in different ranges and to follow Weibull distribution, respectively. Based on the statistical data from a number of commercial catalysts, strength failure probability is proposed as the critical parameter for quality control. Catalyst tablet texture is examined, and it is observed that the tablets with strength close to low end of strength distribution have higher porosity, lower density and larger pore size in comparison with those near high end. For catalyst tablets, low strength is related to increased risk of strength failure, and high strength would result in lower catalyst efficiency. Catalyst tablet strength distributed in a narrow window is beneficial for commercial application. A correlation between catalyst tablet density and strength is established using a model proposed by Knudsen. Results obtained by analysing these interrelated parameters indicate that optimisation of catalyst tablet mechanical strength can be achieved through monitoring and controlling material properties and processing parameters during preparation.