Instituto de Tecnología Química

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and EngineeringGeorge W. Huber, Sara Iborra, and Avelino CormaView Author Information Instituto de Tecnología Químicia, UPV-CSIC, Universidad Politénica de Valencia, Avda. de los Naranjos, s/n, Valencia, Spain Cite this: Chem. Rev. 2006, 106, 9, 4044–4098Publication Date (Web):June 27, 2006Publication History Received3 February 2006Published online27 June 2006Published inissue 1 September 2006https://pubs.acs.org/doi/10.1021/cr068360dhttps://doi.org/10.1021/cr068360dresearch-articleACS PublicationsCopyright © 2006 American Chemical SocietyRequest reuse permissionsArticle Views61161Altmetric-Citations6513LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Alcohols,Biofuels,Biomass,Catalysts,Fossil fuels Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemical Routes for the Transformation of Biomass into ChemicalsAvelino Corma, Sara Iborra, and Alexandra VeltyView Author Information Instituto de Tecnología Química, UPV-CSIC, Universidad Politécnica de Valencia, Avenida de los Naranjos, s/n, Valencia, Spain Cite this: Chem. Rev. 2007, 107, 6, 2411–2502Publication Date (Web):May 30, 2007Publication History Received31 January 2007Published online30 May 2007Published inissue 1 June 2007https://pubs.acs.org/doi/10.1021/cr050989dhttps://doi.org/10.1021/cr050989dresearch-articleACS PublicationsCopyright © 2007 American Chemical SocietyRequest reuse permissionsArticle Views55308Altmetric-Citations5138LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Alcohols,Carbohydrates,Catalysts,Lipids,Selectivity Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFrom Microporous to Mesoporous Molecular Sieve Materials and Their Use in CatalysisAvelino CormaView Author Information Instituto de Tecnología Química, UPV-CSIC, Universidad Politécnica de Valencia, Avda. de los Naranjos s/n, 46022 Valencia, SpainCite this: Chem. Rev. 1997, 97, 6, 2373–2420Publication Date (Web):October 1, 1997Publication History Received7 April 1997Revised16 June 1997Published online1 October 1997Published inissue 1 October 1997https://pubs.acs.org/doi/10.1021/cr960406nhttps://doi.org/10.1021/cr960406nresearch-articleACS PublicationsCopyright © 1997 American Chemical SocietyRequest reuse permissionsArticle Views29508Altmetric-Citations5085LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Catalysts,Materials,Porous materials,Surfactants,Zeolites Get e-Alerts

Simulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTEngineering Metal Organic Frameworks for Heterogeneous CatalysisA. Corma*, H. García, and F. X. Llabrés i XamenaView Author Information Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia, Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos s/n, 46022 Valencia, Spain* To whom correspondence should be addressed. E-mail: [email protected]Cite this: Chem. Rev. 2010, 110, 8, 4606–4655Publication Date (Web):April 1, 2010Publication History Received2 December 2009Published online1 April 2010Published inissue 11 August 2010https://pubs.acs.org/doi/10.1021/cr9003924https://doi.org/10.1021/cr9003924review-articleACS PublicationsCopyright © 2010 American Chemical SocietyRequest reuse permissionsArticle Views38208Altmetric-Citations3174LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Catalysts,Ligands,Materials,Metal organic frameworks,Metals Get e-Alerts

This critical review is intended to attract the interest of organic chemists and researchers on green and sustainable chemistry on the catalytic activity of supported gold nanoparticles in organic transformations. In the general part of this critical review, emphasis is given to the different procedures to form supported gold nanoparticles and to the importance of the support cooperating in the catalysis. Also the convergence of homogeneous and heterogeneous catalysis in the study of gold nanoparticles has been discussed. The core part of this review is constituted by sections in which the reactions catalyzed by supported gold nanoparticles are described. Special emphasis is made on the unique ability of gold catalysts to promote additions to multiple C-C bonds, benzannulations and alcohol oxidation by oxygen (282 references).

The selective reduction of a nitro group when other reducible functions are present is a difficult process that often requires stoichiometric amounts of reducing agents or, if H2 is used, the addition of soluble metals. Gold nanoparticles supported on TiO2 or Fe2O3 catalyzed the chemoselective hydrogenation of functionalized nitroarenes with H2 under mild reaction conditions that avoided the accumulation of hydroxylamines and their potential exothermic decomposition. These chemoselective hydrogenation gold catalysts also provide a previously unknown route for the synthesis of the industrially relevant cyclohexanone oxime from 1-nitro-1-cyclohexene.

In this work some relevant processes for the preparation of liquid hydrocarbon fuels and fuel additives from cellulose, hemicellulose and triglycerides derived platform molecules are discussed. Thus, it is shown that a series of platform molecules such as levulinic acid, furans, fatty acids and polyols can be converted into a variety of fuel additives through catalytic transformations that include reduction, esterification, etherification, and acetalization reactions. Moreover, we will show that liquid hydrocarbon fuels can be obtained by combining oxygen removal processes (e.g. dehydration, hydrogenolysis, hydrogenation, decarbonylation/descarboxylation etc.) with the adjustment of the molecular weight via C–C coupling reactions (e.g. aldol condensation, hydroxyalkylation, oligomerization, ketonization) of the reactive platform molecules.

We have seen the work on gold catalysis to increase exponentially
\nin the last few years. This is specifically true for homogeneous
\ngold(I) and some gold(III) catalysts. Despite further
\nexpansion of gold catalysts to form C-O and C-N bonds, new
\ndevelopments are now starting for selective formation of C-S
\nand, especially, C-P, C-Si, and C-B bonds. This is a field that
\nmay offer new possibilities for gold catalysis.

PURPOSE: To adapt the so-called nonlocal means filter to deal with magnetic resonance (MR) images with spatially varying noise levels (for both Gaussian and Rician distributed noise). MATERIALS AND METHODS: Most filtering techniques assume an equal noise distribution across the image. When this assumption is not met, the resulting filtering becomes suboptimal. This is the case of MR images with spatially varying noise levels, such as those obtained by parallel imaging (sensitivity-encoded), intensity inhomogeneity-corrected images, or surface coil-based acquisitions. We propose a new method where information regarding the local image noise level is used to adjust the amount of denoising strength of the filter. Such information is automatically obtained from the images using a new local noise estimation method. RESULTS: The proposed method was validated and compared with the standard nonlocal means filter on simulated and real MRI data showing an improved performance in all cases. CONCLUSION: The new noise-adaptive method was demonstrated to outperform the standard filter when spatially varying noise is present in the images.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLewis Acids: From Conventional Homogeneous to Green Homogeneous and Heterogeneous CatalysisAvelino Corma and Hermenegildo GarcíaView Author Information Instituto de Tecnología Química CSIC-UPV, Avenida de los Naranjos s/n, Universidad Politécnica de Valencia, 46022 Valencia, Spain Cite this: Chem. Rev. 2003, 103, 11, 4307–4366Publication Date (Web):October 23, 2003Publication History Received28 March 2003Published online23 October 2003Published inissue 1 November 2003https://pubs.acs.org/doi/10.1021/cr030680zhttps://doi.org/10.1021/cr030680zresearch-articleACS PublicationsCopyright © 2003 American Chemical SocietyRequest reuse permissionsArticle Views22611Altmetric-Citations968LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Catalysts,Hydrocarbons,Lewis acids,Oxides,Solvents Get e-Alerts

Metal-organic frameworks (MOFs) are crystalline porous materials formed from bi- or multipodal organic linkers and transition-metal nodes. Some MOFs have high structural stability, combined with large flexibility in design and post-synthetic modification. MOFs can be photoresponsive through light absorption by the organic linker or the metal oxide nodes. Photoexcitation of the light absorbing units in MOFs often generates a ligand-to-metal charge-separation state that can result in photocatalytic activity. In this Review we discuss the advantages and uniqueness that MOFs offer in photocatalysis. We present the best practices to determine photocatalytic activity in MOFs and for the deposition of co-catalysts. In particular we give examples showing the photocatalytic activity of MOFs in H2 evolution, CO2 reduction, photooxygenation, and photoreduction.

Ceria nanoparticles as a support stabilize positive gold species and provide oxygen vacancies. The resulting solid exhibits an exceedingly high efficiency for the solventless aerobic oxidation of primary and secondary alcohols to carbonyl compounds (see picture). The selective oxidation of alcohols is one of the most challenging reactions in green chemistry.1–4 An ideal green oxidation process should involve a highly active and selective recyclable catalyst that is able to work at atmospheric pressure in the presence of oxygen and the absence of solvents and bases.5 Stoichiometric oxidations using transition metal compounds or sulfoxides (Swern oxidation) are still commonly used, despite the formation of a large amount of undesirable products. Several homogeneous Pd-, Cu-, or Ru-based catalysts are able to perform the selective oxidation of alcohols, but they require the use of organic solvents or high oxygen pressure.6–11 From the point of view of heterogeneous catalysis, probably the best system has been reported recently by Kaneda et al.,12 where a palladium-containing apatite is able to oxidize alcohols at atmospheric oxygen pressure even in the absence of solvents. Mizuno et al.13, 14 have described a ruthenium-containing solid catalyst that is able to selectively produce carbonyl compounds from alcohols in the presence of oxygen at atmospheric pressure. Other solid catalysts based on hydrotalcites,15 apatites and mixed oxides,16 or supported Pt and Pd17, 18 have also been studied. Small-crystal-size gold supported on inorganic oxides or active carbon has recently attracted considerable attention since these catalysts are able to promote the selective oxidation of alcohols.19–25 Taking into account that inorganic oxides contain some sites that are able to oxidize alcohols stoichiometrically, it appeared to us that a new concept of catalyst could be put forward if these stoichiometric sites can be converted into catalytic sites by introducing a solid co-catalyst that facilitates the reoxidation of the intermediate metal hydrides to water and the original inorganic oxide. To prove this concept we selected cerium oxide, which contains stoichiometric oxidation sites of alcohols, and cationic gold, which is a metal that transfers hydrides reversibly. In particular, the combination26 of small-crystal-size gold (2–5 nm) and nanocrystalline ceria (≈5 nm) turned out to give a highly active, selective, and recyclable catalyst for the oxidation of alcohols into aldehydes and ketones with high turnover numbers (TON) and frequencies (TOF) using oxygen at atmospheric pressure as oxidant in the absence of solvent and base. Pure, nanocrystalline cerium oxide contains sites that are able to perform the oxidation of alcohols in a stoichiometric manner. Indeed, when IR experiments were carried out in situ by adsorbing 2-propanol on nanocrystalline cerium oxide (see Supporting Information), two IR bands associated with cerium alkoxide appeared; the growth of a band attributable to cerium hydride, was also observed. The appearance of a carbonyl band indicates that acetone was formed at the same time as the cerium hydride. Upon subsequent introduction of O2 into the IR cell at room temperature, the band due to cerium hydride remained unaltered and the formation of water was not observed. These experiments show that cerium oxide alone is able to perform one reaction cycle, but the reduced cerium is stable in the presence of physisorbed O2 and the catalytic cycle is not closed. When gold nanoparticles were deposited onto the nanocrystalline cerium oxide (see Supporting Information for the detailed preparation procedure), the XPS spectrum of the Au 4f7/2 core level shows three bands (see Supporting Information), which correspond to Au3+, Au+, and Au0.27 The presence of cationic gold was also confirmed by the IR band of adsorbed CO (see Supporting Information).28 These results can be rationalized by assuming that the gold nanoparticles formed on the Au⊂CeO2 catalyst (see HRTEM images in the Supporting Information) interact with the nanometric ceria surface, which stabilizes the positive oxidation states of gold26, 29, 30 by creating Ce3+ and oxygen-deficient sites in the ceria. When the anaerobic oxidation of 2-propanol on Au⊂CeO2 was monitored in situ by IR spectroscopy (see Supporting Information) in the same way as with pure nanocrystalline CeO2, the IR bands of the cerium alkoxide and hydride were again observed, and acetone was also formed. However, when O2 was subsequently introduced the metal hydride disappeared and water was formed, contrary to what occurred with CeO2. At this point the cerium oxide is therefore ready to perform another catalytic cycle. After these spectroscopic studies, Au⊂CeO2 was tested as a solid catalyst for the selective aerobic oxidation of a large variety of alcohols. The reactions were performed in a magnetically stirred, glass batch reactor in the absence of solvent and base at 80 °C, with O2 at atmospheric pressure. In other cases the oxidations were also performed in basic water (see Supporting Information for experimental details). High conversions and selectivities were obtained with short reaction times (Table 1). Entry Substrate t [h] Conversion [%] Product Selectivity [%] 1[b] 3-octanol 3.5 97 3-octanone >99 2[c] 3-octanol 2.5 89 3-octanone 96 3[b] 2-phenylethanol 2.5 92 acetophenone 97 4[b] 2,6-dimethylcyclohexanol 2.5 78 2,6-dimethylcyclohexanone 94 5[b] 1-octen-3-ol 3.5 80 1-octen-3-one >99 6[b] cinnamyl alcohol 7 66 cinnamaldehyde 73 7[b] 3,4-dimethoxybenzyl alcohol 7 73 3,4-dimethoxybenzaldehyde 83 8[b] 3-phenyl-1-propanol 6 70 3-phenylpropyl 3-phenylpropanoate 98 9[d] vanillin alcohol 2 96 vanillin 98 10[d] 2-hydroxybenzyl alcohol 2 >99 2-hydroxybenzaldehyde 87 11[d] 3,4-dimethoxybenzyl alcohol 2 >99 3,4-dimethoxybenzylic acid >99 12[d] cinnamyl alcohol 3 >99 cinnamylic acid 98 13[e] n-hexanol 10 >99 hexanoic acid >99 14[d] 2-phenylethanol 5 >99 acetophenone 51 The benefit of using nanoparticles of CeO2 as a support for the gold becomes obvious when comparing the activity (TOF) of Au⊂CeO2 with the activities of Au supported on conventional CeO2 (Au/CeO2), Au/carbon (Au/C) (see Supporting Information for experimental details of the preparation), Au/TiO2, and Au/Fe2O3 (these two last catalysts were supplied by the International Gold Council; Figure 1).31 Note that Au⊂CeO2 is active for the oxidation of alcohols in the absence of solvent and base, conditions under which most other supported gold catalysts are inefficient.5 For instance, Au/C does not catalyze oxidation reactions in the absence of base and water. Turnover frequencies for the oxidation of 3-octanol, given as the ratio of moles of 3-octanone per mole of Au per hour, measured at t=10 min (see Table 1 for reaction conditions). Secondary alcohols can be oxidized with essentially complete conversion and high selectivities on Au⊂CeO2 in the absence of solvent, and benzylic or allylic alcohols are selectively oxidized to the corresponding unsaturated aldehydes, although longer reaction times are required. Aliphatic primary alcohols are more reluctant to undergo oxidation in the absence of solvent. Notably, they give predominantly the corresponding ester with high selectivity, accompanied by lesser amounts of the aldehyde. We have found that esters are directly formed via the hemiacetal, which is detectable by 1H NMR spectroscopy, as indicated in Scheme 1. Indeed, we have seen that the introduction of trimethyl orthoformate, which acts as a scavenger for aldehydes, into the reaction mixture gives the dimethyl acetal of the aldehyde with very high selectivity and completely inhibits the formation of the ester. Note that Au⊂CeO2 is also very active for the oxidation of alcohols in basic aqueous solution. In this case pH plays an important role, with the TOF decreasing upon lowering the pH. In basic aqueous solution, the oxidation of primary alcohols gives the carboxylic acids rather than the esters. Reaction route proposed for the formation of esters in the oxidation of primary alcohols. On the basis of the Au⊂CeO2 characterization and IR study, a reasonable mechanism for the catalytic reaction is depicted in Scheme 2. According to this mechanism, the interaction between gold and ceria will give rise to an important population of positively charged gold and Ce3+ species (detectable by XPS; step 1). The alcohol or the corresponding alkoxide will then react with the Lewis acid sites of Au⊂CeO2 to give a metal alkoxide (step 2), which subsequently undergoes a rapid hydride transfer from CH to Ce3+ and Au+ to give the ketone and CeH (indicated as LAH in Scheme 2) and AuH (as observed by IR spectroscopy; step 3). Upon admission of oxygen into the system and coordination to the oxygen-deficient sites of ceria, formation of cerium-coordinated superoxide (CeOO.) species occurs (step 4).32 These superoxide species evolve into cerium hydroperoxide by hydrogen abstraction from AuH (step 5), and are responsible for the formation, after reduction of CeIV, of the initial Au+ species. The absence of gold would render this step impossible and lead to a depletion of CeIII. This mechanism is compatible with the lack of influence of an excess of TEMPO in the reaction (see footnote [e] in Table 1), since TEMPO is not able to quench oxygen-centered radicals. Proposed mechanism for the oxidation of alcohols in the presence of Au⊂CeO2 as the catalyst. LA=Lewis acid. Kaneda et al. have reported recently that Pd supported on hydroxyapatite is the most active solid catalyst, with a turnover number of 236 000 and a TOF of 9800 h−1.12 We have been able to reproduce these results. Under the reported conditions our catalyst gives a TOF of 12 500 h−1 for the conversion of 1-phenylethanol into acetophenone at 160 °C, with greater than 99 % selectivity for the desired product. The catalyst is fully recyclable after filtering and washing (NaOH 0.5 M), with a TON of 250 000 after three recycles. This shows that gold, which was previously believed to be of little catalytic interest, can become an interesting oxidation catalyst when combined with the right support. In conclusion, we have shown that gold nanoparticles transform nanocrystalline cerium oxide from a stoichiometric oxidant into a catalytic material for the selective oxidation of primary and secondary alcohols to aldehydes and ketones in the presence of oxygen at atmospheric pressure, with high TOFs and selectivities observed. This catalyst makes the process interesting from both an economic and environmental point of view. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2005/z500382_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions.

The borrowing hydrogen (BH) principle, also called hydrogen auto-transfer, is a powerful approach which combines transfer hydrogenation (avoiding the direct use of molecular hydrogen) with one or more intermediate reactions to synthesize more complex molecules without the need for tedious separation or isolation processes. The strategy which usually relies on three steps, (i) dehydrogenation, (ii) intermediate reaction, and (iii) hydrogenation, is an excellent and well-recognized process from the synthetic, economic, and environmental point of view. In this context, the objective of the present review is to give a global overview on the topic starting from those contributions published prior to the emergence of the BH concept to the most recent and current research under the term of BH catalysis. Two main subareas of the topic (homogeneous and heterogeneous catalysis) have been identified, from which three subheadings based on the source of the electrophile (alkanes, alcohols, and amines) have been considered. Then the type of bond being formed (carbon-carbon and carbon heteroatom) has been taken into account to end-up with the intermediate reaction working in tandem with the metal-catalyzed hydrogenation/dehydrogenation step. The review has been completed with the more recent advances in asymmetric catalysis using the BH strategy.

The present review describes the use of metal-organic frameworks (MOFs) as porous matrices to embed metal nanoparticles (MNPs) and occasionally metal oxide clusters, which are subsequently used as heterogeneous catalysts. The review is organized according to the embedded metal including Pd, Au, Ru, Cu, Pt, Ni and Ag. Emphasis is also given in the various methodologies reported for the formation of the NPs and the characterization techniques. The reactions described with this type of solid catalysts include condensation, hydrogenations, carbon-carbon coupling, alcohol oxidations and methanol synthesis among others. Remaining issues in this field have also been indicated.

Gold nanoparticles supported on P25 titania (Au/TiO(2)) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about -1.14 V). For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (Φ(H2) = 7.5% and Φ(O2) = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C.

Upon light excitation MOF-5 behaves as a semiconductor and undergoes charge separation (electrons and holes) decaying in the microsecond time scale. The actual conduction band energy value was estimated to be 0.2 V versus NHE with a band gap of 3.4 eV. Photoinduced electron transfer processes to viologen generates the corresponding viologen radical cation, while holes of MOF-5 oxidizes N,N,N',N'-tetramethyl-p-phenylenediamine. One application investigated for MOF-5 as a semiconductor has been the shape-selective photocatalyzed degradation of phenol in aqueous solutions.

In this perspective, we highlight the main opportunities of metal organic frameworks (MOFs) as heterogeneous catalysts. Along with our personal view on the most promising catalytic applications, the most important issues that still need to be addressed before commercial implementation of MOF catalysis are discussed.