Furfural production by 'acidic steam stripping' of lignocellulose.

Furfural and acetic acid are produced with approximately 60 and 90 mol % yield, respectively, upon stripping bagasse with a gaseous stream of HCl/steam and condensing the effluent to water/furfural/acetic acid. The reaction kinetics is 1(st)  order in furfural and 0.5(th)  order in HCl. A process concept with full recycling of the reaction effluents is proposed to reduce the energy demand to <10 tonsteam tonfurfural (-1) and facilitate the product recovery through a simple liquid/liquid separation of the condensate into a water-rich and a furfural-rich phase.

Profiling physicochemical changes within catalyst bodies during preparation: new insights from invasive and noninvasive microspectroscopic studies.

Cylindrical or spherical catalyst bodies with sizes ranging from tens of micrometers to a few millimeters have a wide variety of industrial applications. They are crucial in the oil refining industry and in the manufacture of bulk and fine chemicals. Their stability, activity, and selectivity are largely dependent on their preparation; thus, achieving the optimum catalyst requires a perfect understanding of the physicochemical processes occurring in a catalyst body during its synthesis. The ultimate goal of the catalyst researcher is to visualize these physicochemical processes as the catalyst is being prepared and without interfering with the system. In order to understand this chemistry and improve catalyst design, researchers need better, less invasive tools to observe this chemistry as it occurs, from the first stages in contact with a precursor all the way through its synthesis. In this Account, we provide an overview of the recent advances in the development of space- and time-resolved spectroscopic methods, from invasive techniques to noninvasive ones, to image the physicochemical processes taking place during the preparation of catalyst bodies. Although several preparation methods are available to produce catalyst bodies, the most common method used in industry is the incipient wetness impregnation. It is the most common method used in industry because it is simple and cost-effective. This method consists of three main steps each of which has an important role in the design of a catalytic material: pore volume impregnation, drying, and thermal treatment. During the impregnation step, the interface between the support surface and the precursor of the active phase at the solid-liquid interface is where the critical synthetic chemistry occurs. Gas-solid and solid-solid interfaces are critical during the drying and thermal treatment steps. Because of the length scale of these catalyst bodies, the interfacial chemistry that occurs during preparation is space-dependent. Different processes occurring in the core or in the outer rim of the catalytic solid are enhanced by several factors, such as the impregnation solution pH, the metal ion concentration, the presence of organic additives, and the temperature gradients inside the body. Invasive methods for studying the molecular nature of the metal-ion species during the preparation of catalyst bodies include Raman, UV-vis-NIR, and IR microspectroscopies. Noninvasive techniques include magnetic resonance imaging (MRI). Synchrotron-based techniques such as tomographic energy dispersive diffraction imaging (TEDDI) and X-ray microtomography for noninvasive characterization are also evaluated.

Tomographic energy dispersive diffraction imaging to study the genesis of Ni nanoparticles in 3D within gamma-Al2O3 catalyst bodies.

Tomographic energy dispersive diffraction imaging (TEDDI) is a recently developed synchrotron-based characterization technique used to obtain spatially resolved X-ray diffraction and fluorescence information in a noninvasive manner. With the use of a synchrotron beam, three-dimensional (3D) information can be conveniently obtained on the elemental composition and related crystalline phases of the interior of a material. In this work, we show for the first time its application to characterize the structure of a heterogeneous catalyst body in situ during thermal treatment. Ni/gamma-Al(2)O(3) hydrogenation catalyst bodies have been chosen as the system of study. As a first example, the heat treatment in N(2) of a [Ni(en)(3)](NO(3))(2)/gamma-Al(2)O(3) catalyst body has been studied. In this case, the crystalline [Ni(en)(3)](NO(3))(2) precursor was detected in an egg-shell distribution, and its decomposition to form metallic Ni crystallites of around 5 nm was imaged. In the second example, the heat treatment in N(2) of a [Ni(en)(H(2)O)(4)]Cl(2)/gamma-Al(2)O(3) catalyst body was followed. The initial [Ni(en)(H(2)O)(4)]Cl(2) precursor was uniformly distributed within the catalyst body as an amorphous material and was decomposed to form metallic Ni crystallites of around 30 nm with a uniform distribution. TEDDI also revealed that the decomposition of [Ni(en)(H(2)O)(4)]Cl(2) takes place via two intermediate crystalline structures. The first one, which appears at around 180 degrees C, is related to the restructuring of the Ni precursor on the alumina surface; the second one, assigned to the formation of a limited amount of Ni(3)C, is observed at 290 degrees C.

Magnetic resonance imaging studies on catalyst impregnation processes: discriminating metal ion complexes within millimeter-sized gamma-Al2O3 catalyst bodies.

Magnetic resonance imaging (MRI) was used to study the impregnation step during the preparation of Ni/gamma-Al(2)O(3) hydrogenation catalysts with Ni(2+) metal ion present in different coordinations. The precursor complexes were [Ni(H(2)O)(6)](2+) and [Ni(edtaH(x))]((2-x)-) (where x = 0, 1, 2 and edta = ethylenediaminetetraacetic acid), representing a nonshielded and a shielded paramagnetic complex, respectively. Due to this shielding effect of the ligands, the dynamics of [Ni(H(2)O)(6)](2+) or [Ni(edtaH(x))]((2-x)-) were visualized applying T(2) or T(1) image contrast, respectively. MRI was applied in a quantitative manner to calculate the [Ni(H(2)O)(6)](2+) concentration distribution after impregnation when it was present alone in the impregnation solution, or together with the [Ni(edtaH(x))]((2-x)-) species. Moreover, the combination of MRI with UV-vis microspectroscopy allowed the visualization of both species with complementary information on the dynamics and adsorption/desorption phenomena within gamma-Al(2)O(3) catalyst bodies. These phenomena yielded nonuniform Ni distributions after impregnation, which are interesting for certain industrial applications.

Monitoring transport phenomena of paramagnetic metal-ion complexes inside catalyst bodies with magnetic resonance imaging.

An indirect magnetic resonance imaging (MRI) method has been developed to determine in a noninvasive manner the distribution of paramagnetic Co2+ complexes inside Co/Al2O3 catalyst extrudates after impregnation with Co2+/citrate solutions of different pH and citrate concentrations. UV/Vis/NIR microspectroscopic measurements were carried out simultaneously to obtain complementary information on the nature of the Co2+ complexes. In this way, it could be confirmed that the actual distribution of Co2+ inside the extrudates could be derived from the MRI images. By combining these space- and time-resolved techniques, information was obtained on both the strength and the mode of interaction between [Co(H2O)6]2+ and different Co2+ citrate complexes with the Al2O(3) support. Complexation of Co2+ by citrate was found to lead to a stronger interaction of Co with the support surface and formation of an eggshell distribution of Co2+ complexes after impregnation. By addition of free citrate and by changing the pH of the impregnation solution, it was possible to obtain the rather uncommon egg-yolk and egg-white distributions of Co2+ inside the extrudates after impregnation. In other words, by carefully altering the chemical composition and pH of the impregnation solution, the macrodistribution of Co2+ complexes inside catalyst extrudates could be fine-tuned from eggshell over egg white and egg yolk to uniform.