A simple, four-step method for better introducing undergraduate students to the fundamentals of molecular orbital (MO) theory of the polyatomic molecules H2O, NH3, BH3 and SiH4 using group theory is reported. These molecules serve to illustrate the concept of ligand group orbitals (LGOs) and subsequent construction of MO energy diagrams on the basis of molecular symmetry requirements.

We describe herein the synthesis and characterization of the complexes KNiF3, [Ni(en)3]I2, [Ni(en)3]Cl2, [Ni(acac)2(H2O)2], [Ni(en)2(H2O)2]Cl2 and [Ni(NH3)6](BF4)2 (en = ethylenediamine, acac- = acetylacetonate) performed in the inorganic synthesis major course at the Chemistry Institute of UFRGS (Universidade Federal do Rio Grande do Sul). The compounds were characterized by infrared and electronic spectroscopy and the electrolytic conductivity was measured. The parameters 10Dq and B were obtained from the electronic spectra and the nefelauxetic and spectrochemical series were determined. The obtained spectrochemical series was F- < acac- < NH3 < en and the nefeulaxetic series was en < NH3 < acac- < F-.

Catalisadores Pd/γ-Al2O3 com dois tamanhos de partículas metálicas foram preparados a partir de [Pd(acac)2]. Subsequentemente, a reação fotoquímica de [M(CO)6] (M = Mo ou W) na presença de Pd/γ-Al2O3 foi usada para preparar catalisadores bimetálicos Pd-M/γ-Al2O3. Os espectros DRIFTS-IVTF das superfícies destes catalisadores antes da decomposição térmica mostraram espécies subcarbonilas [M(CO)n] instáveis. Resultados de quimissorção e adsorção de CO/NO indicaram um bloqueio dos sítios ativos do paládio quando o segundo metal foi incorporado. A atividade catalítica e a seletividade para N2 e O2 na reação NO/CO foram maiores para Pd com maior tamanho de partícula, mas foram inibidas quando Mo ou W foram incorporados. Por outro lado, quando esses catalisadores foram testados para a decomposição de NO, a presença de Mo ou W levou a um aumento da atividade catalítica e da seletividade, com os melhores resultados observados na presença de Mo.

Pd/γ-Al2O3 catalysts with two different metal particle sizes were prepared from [Pd(acac)2]. Subsequently, the photochemical reaction of [M(CO)6] (M = Mo or W) in the presence of Pd/γ-Al2O3 was used to prepare bimetallic Pd-M/γ-Al2O3 catalysts. DRIFTS FTIR spectra of the catalyst surfaces prior to thermal decomposition showed unstable subcarbonyl [M(CO)n] species. Chemisorption and CO/NO adsorption results indicated a blockage of the Pd active sites when the second metal was incorporated. The catalytic activity and the selectivity for the NO/CO reaction were higher for Pd with higher particle size, but they were both inhibited when Mo or W were incorporated. On the other hand, when the catalysts were tested for NO decomposition, the presence of Mo or W led to an increase in the catalytic activity, with optimal results observed in the presence of Mo.

Aluminum oxide was dispersed on a commercial silica gel surface, using successive grafting reactions. The reaction products were characterized by N2 adsorption-desorption isotherms, scanning electron microscopy and infrared spectroscopy. The progressive incorporation of aluminum, up to 5.5% (w/w), does not produce agglomeration of alumina, since changes in the original pore size distribution of the silica matrix were not observed. The aluminum oxide covers homogeneously the silica surface.

Neste trabalho foram estudados catalisadores Ag/Al2O3 e Ag/Al2O3/Corderita, preparados por um método de impregnação convencional, na reação de redução de NO utilizando propeno como agente redutor. Os catalisadores foram caracterizados por redução a temperatura programada (RTP), quimissorção de oxigênio e área superficial, pelo método BET. A atividade catalítica foi determinada utilizando uma mistura reacional contendo 100 ppm de NO, 250 ppm de C3H6 e 2% de oxigênio e uma velocidade espacial de 100000 h-1. Os produtos da reação foram estudados por FTIR. Os resultados dos testes catalíticos mostraram 56% de conversão de NO para o catalisador 2,22%Ag/Al2O3 a 723 K. Os catalisadores de cordierita apresentaram um comportamento semelhante, mas a temperatura de máxima conversão de NO deslocou-se para temperaturas menores.

In this study, a Ag/Al2O3 and Ag/Al2O3/Cordierite catalyst was prepared by a conventional impregnation method and NOx reduction investigated using propylene as a reducing agent. The catalysts were characterized by Temperature Programmed Reduction (TPR), oxygen chemisorption and surface area, using the standard BET method. The catalytic activities were measured under the same reaction conditions, i.e., 100 ppm NO, 250 ppm C3H6, 2% of oxygen and 100000 h-1 space velocity. The reaction products were analyzed by FTIR. The results of the catalytic activity obtained for the 2.22%Ag/Al2O3 catalyst showed 56% NO conversion at 723 K. The catalysts based on Cordierite presented an analogous behavior, but the temperature of maximum NO conversion was lower (620 K).

As reatividades dos sistemas [WCl4(OAr)2] (OAr = O-2,6-C3H3Cl2, O-2,6-C6H3F2 e O-C6H3Me2), juntamente com os compostos de silício Ph2SiH2 e polimetilidrosiloxano (PMHS), foram estudadas em reações de metátese. As olefinas usadas foram 10-undecenoato de metila e 1-hexeno. Os resultados mostraram que os sistemas [WCl4(OAr)2]-composto de silício são ativos e seletivos quando os ligantes arilóxidos possuem grupos eletronegativos em suas estruturas. O composto de silício PMHS apresentou os melhores resultados, mesmo com o composto [WCl4(O-2,6-C6H3Me 2)2], que não possui substituintes eletronegativos. Por ser não-tóxico, não-volátil, barato e de fácil manuseio, PMHS é uma boa alternativa como cocatalisador em reações de metátese.

The reactivity of the [WCl4(OAr)2] (OAr = O-2,6-C3H3Cl2, O-2,6-C6H3F2 and O-C6H3Me2) systems, plus the silicon compounds Ph2SiH2 and polymethylhydrosiloxane (PMHS), were studied in metathesis reactions. The olefins used were methyl-10-undecenoate and 1-hexene. The results showed that the [WCl4(OAr)2]-silicon compound systems are active and selective when the aryloxide ligand contain electronegative groups. The silicon compound PMHS proved to be the best cocatalyst for metathesis, even with the [WCl4(O-2,6-C6H3Me 2)2] compound, which has no electronegative substituents. Because it is non-toxic, non-volatile, easy to handle and cheap, PMHS is a good alternative cocatalyst in metathesis reactions.

The kinetic parameters for the CO oxidation reaction using copper/alumina-modified ceria as catalysts were determined. The catalysts with different concentrations of the metals were prepared using impregnation methods. In addition, the reduction-oxidation behaviour of the catalysts were investigated by temperature-programmed reduction. The activity results show that the mechanism for CO oxidation is bifunctional : oxygen is activated on the anionic vacancies of ceria surface, while carbon monoxide is adsorbed preferentially on the higher oxidation copper site. Therefore, the reaction occurs on the interfacial active centers. Temperatures-programmed Reduction patterns show a higher disperdion when cerium oxide is present.